H I S O F T ZX Spectrum Programmer's Manual D E V P A C (C) Hisoft 1985 (Typed in 1998 by Nele Abels-Ludwig. Help to keep Spectrum software usable. Transcribe technical manuals!) Contents Page -------- ---- PART 1 GENS3 SECTION 1 GETTING STARTED 1 SECTION 2 DETAILS OF GENS3 3 2.0 How GENS3 works 3 2.1 Assembler Statement Format 6 2.2 Labels 7 2.3 Location Counter 8 2.4 Symbol Table 8 2.5 Expressions 9 2.6 Macros 10 2.7 Assembler Directives 12 2.8 Conditional Pseudo-Mnemonics 14 2.9 Assembler Commands 14 SECTION 3 THE INTEGRAL EDITOR 19 3.1 Introduction to the Editor 19 3.2 The Editor Commands 20 3.2.1 Text Insertion 20 3.2.2 Text Listing 21 3.2.3 Text Editing 22 3.2.4 Tape/Microdrive Commands 24 3.2.5 Assembling and Running 26 3.2.6 Other Commands 26 3.3 An Example Using the Editor 28 APPENDIX 1 ERROR NUMBERS AND THEIR MEANINGS 31 APPENDIX 2 RESERVED WORDS, MNEMONICS ETC. 32 APPENDIX 3 A WORKED EXAMPLE 33 APPENDIX 4 AN EXTENDED CAT PROGRAM 39 PART 2 MONS3 SECTION 1 GETTING STARTED 45 SECTION 2 THE COMMANDS AVAILABLE 47 Flip Base 47 Page Disassembly 47 Increment MP by 1 47 Decrement MP by 1 47 Decrement MP by 8 47 Increment MP by 8 47 Update MP to SP 47 Get a Pattern 48 Decimal to Hexadecimal 48 Intelligent Copy 48 Jump to Address 49 Continue Execution 49 List Memory 50 Set Memory Pointer (MP) 50 Get Next Pattern 50 Go Relative 51 Fill Memory 51 Flip Register Display 52 Set a Breakpoint and Continue 52 Block Disassembly 52 Reverse Relative 55 Reverse Absolute 55 Set a Breakpoint 56 Go Absolute 57 Enter ASCII into Memory 57 Single-Step 57 Example Session 58 Print Memory 61 Modifying Memory 61 Modifying Registers 61 APPENDIX AN EXAMPLE FRONT PANEL DISPLAY 63 - Page 1----------------------------------------------------------------------- HiSoft GENS3 Programmer's Manual SECTION 1 GETTING STARTED Introduction and Loading Instructions ------------------------------------- GENS3 is a powerful and easy-to-use Z80 assembler which is very close to the standard Zilog assembler in definition. Unlike many other assemblers available for microcomputers, GENS3 is an extensive, professional piece of software and you are urged to study the following sections, together with the example in Appendix 3, very carefully before attempting to use the assembler. If you are a complete novice, work through Appendix 3 first. GENS3 is roughly 9K bytes in length, once relocated, and uses its own internal stack so that it is a self-contained piece of software. It contains its own integral line editor which places the textfile immediately after the GENS3 code while the assembler's symbol table is created after the textfile. Thus when loading GENS3 you must allow enough room to include the assembler itself and the maximum symbol table and text size that you are likely to use in the current session. It will often be convenient, therefore, to load GENS3 into low memory. To load GENS3 proceed as follows: Place the supplied tape in your cassette recorder, type: LOAD "" CODE xxxxx and press PLAY on the recorder - where xxxxx is the decimal address at which you want GENS3 to run. Once you have loade the GENS3 code into the computer you may enter the assembler by RANDOMIZE USR xxxxx where xxxxx is the address at which you loaded the assembler code. If at any subsequent time you wish to re-enter the assembler then you should execute the address xxxxx + 56 for a cold start (destroying any text) or address xxxxx for a warm start (preserving any previously created textfile). For example, say you want to load GENS3 so that it executes from address 26000 decimal - proceed as follows: LOAD "" CODE 26000 RANDOMIZE USR 26000 To re-enter the assembler use RANDOMIZE USR 26056 for a cold start and RANDOMIZE USR 26000 for a warm start. Once you have entered GENS3, you will be prompted with a '>' sign, the editor's command prompt - consult Section 3 for how to enter and edit text and Section 2 for what to enter. - Page 2 ---------------------------------------------------------------------- Making a Backup Copy -------------------- Once you have loaded GENS3 into your Spectrum's memory then you can make a backup copy of the assembler as follows: SAVE "GENS3" CODE xxxxx,10034 to cassette SAVE*"M";1;"GENS3" CODE xxxxx,10034 to Microdrive where: xxxxx is the address at which you loaded GENS3. Please note that we allow you to make a backup copy of GENS3 for your own use so that you can program with confidence. Please do not copy GENS3 to give (or worse, sell) to your friends, we supply very reasonably priced software and a full after-sales support service but if enough people copy our software we shall not be able to continue this; please buy, don't steal. - Page 3 ---------------------------------------------------------------------- SECTION 2 DETAILS OF GENS3 2.0 How GENS3 Works, Assembler Options, Listing Format etc. ----------------------------------------------------------- GENS3 is a fast, two-pass Z80 assembler which assembles all standard Z80 menmonics and has added features which include macros, conditional assembly, many assembler commands and a binary-tree symbol table. When you invoke an assembly (using the editor 'A' command - see Section 3) you will first be asked to specify 'Table size: ' in decimal. This is the amount of space that will be allocated to the symbol table during the assembly. If you default (by simply hitting ENTER) then GENS3 will choose a symbol table size that it thinks is suitable for the size of the text - normally this will be perfectly acceptable. However, when using the 'Include' option, you may have to specify a larger than normal symbol table size; the assembler cannot predict the size of the file that will be included. After 'Table size: ' you will be asked for any 'Options: ' that you require. Enter these in decimal adding the option numbers together if you want more than one option. The options available are: Assembler Options: ------------------ Option 1 Produce a symbol table listing at the end of the second pass of the assembly. Option 2 Do not generate any object code. Option 4 Do not produce an assembly listing. Option 8 Direct any assembly listing to the printer. Option 16 Simply place the object code, if generated, after the symbol table. The Location Counter is still updated, by the ORG so that object code can be placed in one section of memory but designed to run elsewhere. Option 32 Turn off the check of where the object code is going - useful for speeding up assembly. Example: Option 36 produces a fast assembly - no listing is generated and no checks are made to see where the object code is being placed. Note that if you have used Option 16 then the ENT assembler directive will have no effect. You can work out where the object code has been placed if Option 16 has been specified by using the editor 'X' command to find out the end of the text (the second number displayed) and then adding to this the amount of symbol table allocated + 2. - Page 4 ---------------------------------------------------------------------- Assembly takes place in two passes; during the first pass GENS3 searches for errors and compiles the symbol table, the second pass generates object code (if option 2 is not specified). During the first pass nothing is displayed on the screen or printer unless an error is detected, in which case the rogue line will be displayed with an error number below it (see Appendix 1). The assembly is paused - press 'E' to return to the editor or any other key to continue the assembly from the next line. At the end of the first pass the message: Pass 1 errors: nn will be displayed. If any errors have been detected the assembly will then halt and not proceed to the second pass. If any labels were referenced in the operand field but never declared in a label field then the message '*WARNING' label absent' will be displayed for each missing label declaration. It is during the second pass that object code is generated (unless generation has been turned off by Option 2 - see above). An assembler listing is generated during this pass unless it has been switched off by Option 4 or the assembler command *L-. The assembler listing is normally of the form: C000 210100 25 label LD HL,1 1 6 15 21 26 The first entry in the line is the value of the Location Counter at the start of processing this line, unless the mnemonic in this line is one of the pseudo-mnemonics ORG, EQU or ENT (see Section 2.7) in which case the first entry will represent the value in the operand field of the instruction. This entry is normally displayed in hexadecimal but may be displayed in unsigned decimal through use of the assembler command *D+ (see Section 2.9) The next entry, from column 6, is up to 8 characters in length (representing up to 4 bytes) and is the object code produced by the current instruction - but see the *C assembler command below. Then comes the line number - an integer in the range 1 to 32767 inclusive. Columns 21-26 of the first line contain the first 6 characters of any label defined in this line. The following two paragraphs apply only to systems with narrow screen widths - on systems with a screen width greater than 40 each assembler listing line is contained wholly on one screen line. - Page 5 ---------------------------------------------------------------------- After any label comes a new line - on this line the mnemonic is displayed from columns 21-24. Then comes the operand field from column 26 of this line and finally any comments that have been inserted at the end of the line with new lines being generated as necessary. The above format aids readability of the assembler listing on such a narrow screen width as that of the SPECTRUM. GENS3 does not re-define the screen width of the SPECTRUM because this would increase the space occupied by GENS3 and would be restrictive in that the standard output routines of the SPECTRUM ROM could not be used. The *C assembler command may be used to produce a shorter assembly listing line - its effect is to omit the 9 characters representing the object code of the line thus enabling most assembler lines to fit on one screen line. See Section 2.8 below. Modifying the Listing Format ---------------------------- It is possible to modify the form in which each line of the listing is split by POKEing 3 locations within GENS3. Details of how to do this are given below. We distinguish between 'assembly line' which is the current line of the assembly listing held in an internal buffer and 'screen line' which is a line that actually appears on the screen. An assembly line will normally generate more than one screen line. 1. Location 'Start of GENS3 + 51 (#33)' dictates at which column position - 5 the first screen line of the assembly line will be terminated. Change this byte to zero to cause the line to wrap round (useful if you have a full-width printer) or any other value (<256) to end the first screen line at a particular column. 2. Location 'Start of GENS3 + 52 (#34)' gives the column position (starting at 1) at which each subsequent screen line of the assembly line is to start. 3. Location 'Start of GENS3 + 53 (#35)' gives how many characters from the remainder of the assembly line are to be displayed on each screen line after the first screen line. As an example, say ou wanted the first screen line of each assembly line to contain 20 characters (i.e. not including the label field) and then each subsequent screen line to start at column 1 and fill the whole line. Also assume that you have loaded GENS3 at 26000 decimal. To effect these changes, execute the following POKE instructions from within BASIC: POKE 26051,20 POKE 26052,1 there must be at least one space at the POKE 26053,31 start of the subsequent screen line. - Page 6 ---------------------------------------------------------------------- The above modifications are only applicable if the *C command has not been used - use of the *C command causes lines to roll over where necessary. The assembly listing may be paused at the end of a line by hitting CAPS SHIFT and SPACE together - subsequently hit 'E' to return to the editor or any other key to continue the listing. The only errors that can occur during the second pass are *ERROR* 10 (see Appendix 1) and 'Bad ORG!' (which occurs when the object code will overwrite GENS3, the textfile or the symbol table - the detection of this can be turned off by Option 32. *ERROR* 10 is non-fatal and you may continue the assembly as for first pass errors, whereas 'Bad ORG!' is fatal and immediately returns control to the editor. At the end of the second pass the message: Pass 2 errors: nn will be displayed followed by warnings of any absent labels - see above. The following message is now displayed: Table used: xxxxx from yyyyy This informs you of how much of the symbol table was used compared with how much was allocated. At this point, if the assembler directive ENT has been used correctly, the message 'Executes: nnnnn' is displayed. This shows the run address of the object code - you can execute the code by using the editor 'R' command. Be careful using the 'R' command unless you have just finished a successful assembly and seen the 'Executes: nnnnn' message. Finally, if option 1 has been specified, an alphabetic list of the labels used and their associated values will be produced. The number of entries displayed on one line may be changed by POKEing 'Start of GENS3 + 50' with the relevant value; the default is 2. Control now returns to the editor. 2.1 Assembler Statement Format. ------------------------------- Each line of text that is to be processed by GENS3 should have the following format where certain fields are optional: LABEL MNEMONIC OPERANDS COMMENT start LD HL,label ;pick up 'label' Spaces and tab characters (inserted by the editor) are generally ignored. - Page 7 ---------------------------------------------------------------------- The line is processed in the following way: The first character of the line is checked and subsequent action depends on the nature of this character as indicated below: ';' the whole line is treated as a comment i.e. effectively ignored. '*' expects the next character(s) to constitute an assembler command (see Section 2.8). Treats all characters after the command as a comment. (end-of-line character) simply ignores the line. ' ' (space or tab) if the first character is a space or a tab character then GENS3 expects the next non-space or non-tab character to be the start of a Z80-mnemonic. If the first character of a line is any character other than those given above then the assembler expects a label to be present - see Section 2.2. After processing a valid label, or if the first character of the line is a space/tab, the assembler searches for the next non-space/tab character and expects this to be either an end-of-line character or the start of a Z80-mnemonic (see Appendix 2) of up to 4 characters in length and terminated by a space/tab or end-of-line character. If the mnemonic is valid and requires one or more operands then spaces/tabs are skipped and the operand field is processed. Labels may be present alone in an assembler statement; this is useful for increasing the readability of the listing. Comments may occur anywhere after the operand field or, if a mnemonic takes no arguments, after the mnemonic field. 2.2 Labels. ----------- A label is a symbol which represents up to 16 bits of information. A label can be used to specify the address of a particular instruction or data area or it can be used as a constant via the EQU directive (see Section 2.7). If a label is associated with a value greater than 8 bits and it is then used in a context where an 8 bit constant is applicable then the assembler will generate an error message e.g. label EQU #1234 LD A,label will cause *ERROR* 10 to be generated when the second statement is processed during the second pass. - Page 8 ---------------------------------------------------------------------- A label may contain any number of valid characters (see below) although only the first 6 are treated as significant; these first 6 characters must be unique since a label cannot be re-defined (*ERROR* 4). A label must not constitute a reserved word (see Appendix 2) although a reserved word may be embedded as part of a label. The characters which may be legally used within a label are 0-9, $ and A-z. Note that 'A-z' included all the upper and lower case alphabetics together with the characters [, \, ], ^, # and _. A label must begin with an alphabetic character. Some examples of valid labels are: LOOP loop a_long_label L[1] L[2] a LDIR LDIR is not a reserved word two^5 2.3. Location Counter --------------------- The assembler maintains a location counter so that a symbol in the label field can be associated with an address and entered into the symbo table. This location counter may be set to any value via the ORG assembler directive (see Section 2.7). The symbol '$' can be used to refer to the current value of the location counter e.g. LD HL,$+5 would generate code that would load the register pair HL with a value 5 greater than the current location counter value. 2.4. Symbol Table ----------------- When a label is encountered for the first time it is entered into a table along with two pointers which indicate, at a later time, how this label is related alphabetically to other labels within the table. If the first occurence of the label is in the label field then its value (as given by the location counter of the value of the expression after an EQU assembler directive) is entered into the symbol table. Otherwise the value is entered whenever the symbol is subsequently found in the label field. This type of symbol table is called a binary tree symbol table and its structure enables symbols to be entered into and recovered from the table in a very short time - essential for large programs. The size of an entry in the table varies from 8 bytes to 13 bytes depending on the length of the symbol. - Page 9 ---------------------------------------------------------------------- If, during the first pass, a symbol is defined more than once then an error (*ERROR* 4) will be generated since the assembler does not know which value should be associated with the symbol. If a symbol is never associated with a value then the message '*WARNING* symbol absent' will be generated at the end of the assembly. The absence of a symbol definition does not prevent the assembly from continuing. Note that only the first 6 characters of a symbol are entered into the symbol table in order to keep down the size of the table. At the end of the assembly you will be given a message stating how much memory was used by the symbol table during this assembly - you may change how much memory is allocated to the symbol table by responding to the 'Table: ' prompt when starting the assembly (see Section 2.0). 2.5. Expressions. ----------------- An expression is an operand entry consisting of either a single TERM or a combination of TERMs each seperated by an OPERATOR. The definitions of TERM and PERATOR follow: TERM decimal constant e.g. 1029 hexadecimal constant e.g. #405 binary constant e.g. %10000000101 character constant e.g. "a" label e.g. L1029 also '$' may be used to denote the current value of the location counter. OPERATOR '+' addition '-' substraction '&' logical AND '@' logical OR '!' logical XOR '*' integer multiplication '/' integer division '?' MOD function (a ? b = a - (a/b)*b) Notes: '#' is used to denote the start of a hexadecimal number, '%' for a binary number and '"' for a character constand. When reading a number (decimal, hexadecimal or binary) GENS3 takes the least significant 16 bits of the number (i.e. MOD 65535) e.g. 70016 becomes 4480 and #5A2C4 becomes #A2C4. A wide variety of operators are provided but no operator precedence is observed - expressions are evaluated strictly from left to right. The operators '*', '/' and '?' are provided merely for added convenience and not as part of a full expression handler which would increase the size of GENS3. - Page 10 --------------------------------------------------------------------- If an expression is enclosed within parantheses then it is taken as representing a memory address as in the instruction LD HL,(loc+5) which would lod the register pair HL with the 16 bit value contained at memory location 'loc+5'. Certain Z80 instructions (JR and DJNZ) expect operands which have an 8 bit value and not a 16 bit one - this is called relative addressing. When relative addresses are specified GENS3 automatically substracts the value of the location counter at the NEXT instruction from the value given in the operand field of the current instruction in order to obtain the relative address for the current instruction. The range of values allowd as a relative address are the location counter value of the next instruction -128 to +127. If, instead, you wish to specify a relative offset from the location counter value of the current instruction then you should use the symbol '$' (a reserved word) followed by the required displacement. Since this is now relative to the current instruction's location counter value the displacement must be in the range -126 to +129 inclusive. Examples of valid expressions: #5000 - label %1001101 ! %1011 gives %1000110 #3456 ? #1000 gives #456 4 + 5 * 3 - 8 gives 19 $-label+8 2345 / 7 - 1 gives 334 "A"+128 "y"-";"+7 (5 * label - #1000 & %1111) 17 @ %1000 gives 25 Note that the spaces may be inserted between TERMs and OPERATORs and vice vers but not within TERMs. If a multiplication operation would result in an absolute value greater than 32767 then *ERROR* 15 is reported while if a division operation involves a division by zero then *ERROR* 14 is given - otherwise overflow is ignored. All arithmetic uses the two's complement for where any numbers greater than 32767 are treated as negative e.g. 60000 = -55336 (60000-65536). 2.6 Macros. ----------- Macros allow you to write shorter, more meaningful assembler programs but they must be used with care and must not be confused with subroutines. A macro definition consists of a series of assembler statements, together with the name of the macro; when this macro name is used subsequently in the mnemonic field then - Page 11 --------------------------------------------------------------------- it will be replaced by all the assembler statements that made up the definition e.g. the macro NSUB may be defined thus: NSUB MAC OR A SBC HL,DE ADD HL,DE ENDM and then, whenever NSUB is used as a mnemonic, it will generate the three assembler statements OR A, SBC HL and ADD HL,DE. This saves you typing and makes your program easier to understand but you must remember that every occurence of NSUB results in code being generated and it may be more efficient to use a CALL to a subroutine instead. Below, we give the format of macro definitions and invocation together with some more examples, please study these carefully. A macro definition takes the following form: Name MAC . . macro definition . . ENDM where Name is the macro name that will invoke the text of the macro whenever Name is used subsequently in the mnemonic field, MAC indicates the start of the macro definition and ENDM indicates the end of the definition. Parameters of the macro may be referenced within the macro definition by the use of the equals sign '=' followed by the parameter number (0-31 inclusive). For example, the macro: MOVE MAC LD HL,=0 LD DE,=1 LD BC,=2 LDIR ENDM takes 3 parameters, source address, destination address and length, loads the relevant values in HL, DE and BC and then performs the instruction LDIR. To invoke this macro at a later stage in your program, simply use the name of the macro in the mnemonic field followed by the values that you wish the 3 parameters to take e.g. MOVE 16384,16385,4069 We have used specific addresses in this example but we can, in fact, use any valid expression to specify the value of the macro parameter e.g. - Page 12 --------------------------------------------------------------------- MOVE start,start+1,length Think ... is the above a good use of a macro? Could it have been a subroutine? Within the macro definition, the parameters may appear in any valid expression e.g. HMS MAC LD HL,=0*3600 LD DE,=1*60 ADD HL,DE LD DE,=2 ADD HL,DE ENDM is a macro, taking 3 parameters - hours, minutes, seconds, that produces in register HL the total number of seconds specified by the parameters. You might use it like this: Hours EQU 2 Minutes EQU 30 Seconds EQU 12 Start EQU 0 HMS Hours,Minutes,Seconds LD DE,Start ADD HL,DE ; HL gives the finish time Macros may not be nested so that you cannot define a macro within a macro definition nor can you invoke a macro within a macro definition. At assembly time, whenever a macro name is encountered in the mnemonic field, the text of the macro is then assembled. Normally this text is not listed in the assembly listing - only the macro name is shown. However, you can force a listing of the expansion of the macro by using the assembler command *M+ before you want macro expansions to be listed - subsequently use *M- to switch off this expansion. If you run out of Macro Buffer space then a message will be displayed and the assembly aborted; use the editor's C command after saving your text, to allocate a larger macro buffer. 2.7 Assembler Directives ------------------------ Certain 'pseudo-mnemonics' are recognised by GENS3. These assembler directives, as they are called, have no efect on the Z80 processor at run-time, i.e. they are not decoded into opcodes, they simply direct the assembler to take certain actions at assembly time. These actions have the effect of changing, in some way, the object code produced by GENS3. - Page 13 --------------------------------------------------------------------- Pseudo-menmonics are assembled exactly like executable instructions; they may be preceded by a label (necessary for EQU) and followed by a comment. The directives available are: ORG expression sets the location counter to the value 'expression'. If option 2 and option 16 are both not selected and an ORG would result in the overwriting of the GENS3 program, the textfile or the symbol table then the message 'Bad ORG!' is displayed and the assembly is aborted. See Section 2.0 for more details on how options 2 and 16 affect the use of ORG. EQU expression must be preceded by a label. Sets the value of the label to the value of 'expression'. The expression cannot contain a symbol which has not yet been assigned a value (*ERROR* 13). DEFB expression,expression,... each 'expression' must evaluate to 8 bits; the byte at the address currently held by the location counter is set to the value of 'expression' and the location counter advanced by 1. Repeats for each expression. DEFW expression,expresion,... sets the 'word' (two bytes) at the address currently held by the location counter to the value of 'expression' and advances the location counter by 2. The lesser significant byte is placed first followed by the more significant byte. Repeats for each expression. DEFS expression increases the location counter by the value of 'expression' - equivalent to reserving a block of memory of size equal to the value of expression. DEFM "s" defines the contents of n bytes of memory to be equal to the ASCII representation of the string s, where n is the length of the string and may be, in theory, in the range 1 to 255 inclusive although, in practice, the length of the string is limited by the length of the line you can enter from the editor. The first character in the operand field ('"' above) is taken as the string delimiter and the string s is defined as those characters - Page 14 --------------------------------------------------------------------- between two delimiters; the end-of-line character also acts as a terminator of the string. ENT expression this has no effect on the generated object code, it is simply used to define an address to which the editor's R command will jump to. ENT expression sets this address to the value of expression - used in conjunction with the editor 'R' command (see section 3). There is no default for the execute address. 2.8 Conditional Pseudo-mnemonics. --------------------------------- Conditional pseudo-mnemonics provide the programmer with the capability of including or not including certain sections of source text in the assembly process. This is made available through the use of IF, ELSE and END. IF expression this evaluates 'expression'. If the result is zero then the assembly of subsequent lines is turned off until either an 'ELSE' or an 'END' pseudo-mnemonic is encountered. If the value of 'expression' is non-zero then the assembly continues normally. ELSE this pseudo-mnemonic simply flips the assembly on and off. If the assembly is on before the 'ELSE' is encountered then it will subsequently be turned off and vice versa. END 'END' simply turns the assembly on. Note: Conditional pseudo-mnemonics cannot be nested; no check is made for nested IFs so any attempt to nest these mnemonics will have unspecified results. 2.9. Assembler Commands. ------------------------ Assembler commands, like assembler directives, have no effect on the Z80 processor at runtime since they are not decoded into opcodes. However, unlike assembler directives, they also have no effect on the object code produced by the assembler - assembler commands simply modify the listing format. An assembler command is a line of the source text that begins with an asterisk '*'. The letter after the asterisk determines type of the command and must be in upper case. The remainder - Page 15 --------------------------------------------------------------------- of the line may be any text except that the commands 'L' and 'D' expect a '+' or a '-' after the command. The following commands are available: *E (eject) causes three blank lines to be sent to the screen or the printer - useful for separating modules. *Hs causes string s to be taken as a heading which is printed after each eject (*E). *H automatically performs a *E. *S causes the listing to be stopped at this line. The listing my be reactivated by pressing any key on the keyboard. Useful for reading addresses in the middle of the listing. Note: *S is still recognised after a *L-, *S does not halt printing. *L- causes listing and printing to be turned off beginning with this line. *L+ causes listing and printing to be turned on starting with this line. *D+ causes the value of the location counter to be given in decimal at the beginning of each line instead of the normal hexadecimal. Unsigned decimal is used. *D- reverts to using hexadecimal for the value of the location counter at the start of each line. *C- Shorten the assembler listing starting from the next line. The listing is abbreviated by not including the display of the object code generated by the current line - this saves 9 characters and enables most assembler lines to fit within one 32 character screen line, thus improving readability. *C+ Revert to the full assembler listing as described in Section 2.0. - Page 16 --------------------------------------------------------------------- *M+ Turn on the listing of macro expansions. *M- Turn off the listing of macro expansions. *F {filename} This is a very powerful command which allows you to assemble text from tape to microdrive - the textfile is read from the tape or microdrive into a buffer, a block at a time, and then assembled from the buffer; this allows you to create large amounts of object code since the text being assembled does not take up valuable memory space. The filename (up to 10 characters) of the textfile you wish to 'include' at this point in the assembly may, optionally, be specified after the 'F' and must be preceded with a space. If the file is on microdrive cartridge then you indicate this by starting the filename with a drive number and a colon e.g. *F 2:test to include from Microdrive Drive 2 *F test to include from tape If no filename is given then the first textfile found on the tape is included, this is not allowed for microdrive inclusion. If you are including from microdrive then the text to be included should have been saved previously using the editor's P(ut) command in the normal way. If including from tape then you must have saved the file previously to tape using the editor's 'T' command and not the 'P' command - this is necessary because a textfile to be included from tape must be dumped out in blocks with sufficient length inter-block gaps to allow the assembly of the current block before the next block is loaded from the tape. The size of the block used by this command (and the editor's 'T' command) is set using the editor's 'C' command (see next section). The ability to select the size of this buffer enables you to optimise the size/speed ratio of any inclusion of text from tape; for example if you are not intending to use the 'F command during an assembly then you may find it useful to specify a buffer size of 0 to minimise the space taken up by GENS3 and its workspace. Note that the buffer size specified in the session in which you dumped out a file to be included must be the same as the buffer size given in the session in which you are actuall including the text. - Page 17 --------------------------------------------------------------------- Whenever the assembler detects an 'F' command it searches the tape or microdrive cartridge for the relevant file; this will happen in the first and second passes since the include text must be scanned in each pass. If including from tape, the tape is then searched for an include file with the required filename, or for the first file. If an include file is found whose filename does not match that required then the message 'Found filename' is displaed and the searching continues, otherwise 'Using filename' is displayed, the file loaded, block by block, and included. See Appendix 3 for an example of the use of this command. Assembler commands, other than *F, are recognised only within the second pass. If assembly has been turned off by one of the conditional pseudo-mnemonics then the effect of any assembler command is also turned off. - Page 18 --------------------------------------------------------------------- (blank page) - Page 19 --------------------------------------------------------------------- SECTION 3 THE INTEGRAL EDITOR 3.1 Introduction to the Editor. ------------------------------- The editor supplied with all versions of GENS3 is a simple, line-based editor designed to work with all Z80 operating systems while maintaining ease of use and the ability to edit programs quickly and efficiently. In order to reduce the size of the textfile, a certain amount of compression of spaces is performed by the editor. This takes place according to the following scheme: whenever a line is typed in from the keyboard it is entered, character by character into a buffer internal to the assembler; then, when the line is finished (i.e. you hit ENTER), it is transferred from the buffer into the textfile. It is during this transfer that certain spaces are compressed: the line is scanned from its first character, if this is a space then a tab character is entered into the textfile and all subsequent spaces are skipped. If the first character is not a space then characters are transferred from the buffer to the textfile until a space is detected whereupon the action taken is the the same as if the next character was the first character in the line. This is then repeated a further time with the rsult that tab characters are inserted at the front of the line or between the label and mnemonic and between the mnemonic and the operands and between the operands and any comment. Of course, if any carriage return (ENTER) character is detected at any time then the transfer is finished and control returned to the editor. This compression process is transparent to the user who may simply use tab control characters (CAPS SHIT 8) to produce a neatly tabuleted textfile which, at the same time, is economic on storage. Note that spaces are not compressed within comments and spaces should not be present within a label, mnemonic or operand field. The editor is entered automatically when GENS3 is executed and displays the message: Copyright Hisoft 1983,84 All rights reserved followed by the editor prompt '>'. In response to the prompt you may enter a command line of the following format: C N1,N2,S1,S2 followed by ENTER - Page 20 --------------------------------------------------------------------- C is the command to be executed (see Section 3.2 below). N1 is a number in the range 1-32767 inclusive. N2 is a number in the range 1-32767 inclusive. S1 is a string of characters with a maximum length of 20. S2 is a string of characters with a maximum length of 20. The comma is used to separate the various arguments (although this can be changed - see the 'S' command) and spaces are ignored, except within the strings. None of the arguments are mandatory although some of the commands (e.g. the 'D'elete command) will not proceed without N1 and N2 being specified. The editor remembers the previous numbers and strings that you entered and uses these former values, where applicable, if you do not specify a particular argument within the command line. The values of N1 an N2 are initially set to 10 and the strings are initially empty. If you enter an illegal command line such as F-1,100,HELLO then the line will be ignored and the message 'Pardon?' displayed - you should retype the line correctly e.g. F1,100,HELLO. This error message will also be displayed if the length of S2 exceeds 20; if the length of S1 is greater than 20 then any excess characters are ignored. Commands may be entered in upper or lower case. While entering a command line certain key combinations may be used to edit the line viz. CAPS SHIFT 5 to delete to the beginning of the line, CAPS SHIFT 8 to advance the cursor to the next tab position, CAPS SHIT 0 to delete the previous character. The following sub-section details the various commands available within the editor - note that wherever an argument is enclosed by the symbols '< >' then that argument must be present for the command to proceed. 3.2 The Editor Commands ----------------------- 3.2.1 Text Insertion. Text may be inserted into the textfile either by typing a line number, a space and then the required text or by use of the 'I' command. Note that if you type a line number followed by ENTER (i.e. without any text) then that line will be deleted from the text if it exists. Whenever text is being entered CAPS SHIFT 5 (delete to the beginning of the line), CAPS SHIFT 8 (go to the next tab position) and CAPS SHIFT 1 (return to the command loop) may be employed. The DELETE (CAPS SHIFT 0) key will produce a destructive backspace (but not beyond the beginning of the text line). Text is entered into an internal buffer within GENS3 and if this buffer should become full then you will be prevented from entering any more text - you must then use CAPS SHIFT 0 or CAPS SHIFT 5 to free space in the buffer. - Page 21 --------------------------------------------------------------------- If, during text insertion, the editor detects that the end of text is nearing the top of RAM it displays the message 'Bad Memory!'. This indicates that no more text can be inserted and that the current textfile, or at least part of it, should be saved to tape for later retrieval. Command: I n,m Use of this command gains entry to the automatic insert mode: you are prompted with line numbers starting at n and incrementing in steps of m. You enter the required text after the displayed line number, using the various control codes if desired and terminating the text line with ENTER. To exit from this mode use CAPS SHIFT 1. If you enter a line with a line number that already exists in the text then the existing line will be deleted and replaced with the new line, after you have pressed ENTER. If the automatic incrementing of the line number produces a line number greater than 32767 then the Insert mode will exit automatically. If, when typing in text, you get to the end of a screen line without having entered 64 characters (the buffer size) then the screen will be scrolled up and you may continue typing on the next line - an automatic indentation will be given to the text so that the line numbers are effectively separated from the tet. 3.2.2 Text Listing. Text may be inspected by use of 'L' command; the number of lines displayed at any one time during the execution of this command is fixed initially but may be changed through use of the 'K' command. Command: L n,m This lists the current text to the display device from line number n to line number m inclusive. The default value for n is always 1 and default value for m is always 32767 i.e. default values are not taken from previously entered arguments. To list the entire textfile simply use 'L' without any arguments. Screen lines are formatted with a left hand margin so that the line number is clearly displayed. Tabulation of the line is automatic, resulting in a clear separation of the various fields with the line. The number of screen lines listed on the display device may be controlled through use of the 'K' command - after listing a certain number of lines the list will pause (if not yet at line number m), hit CAPS SHIFT 1 to return to the main editor loop or any other key to continue the listing. - Page 22 --------------------------------------------------------------------- Command: K n 'K' sets the number of screen lines to be listed to the display device before the display is paused as described in 'L' above. The value (n MOD 256) is computed and stored. For example use K5 if you wish a subsequent 'L'ist to produce five screen lines at a time. 3.2.3 Text Editing Once some text has been created there will inevitably be a need to edit some lines. Various commands are provided to enable line to be amended, deleted, moved and renumbered: Command: D All lines from n to m inclusive are deleted from the textfile. If m Use of the 'N' command causes the textfile to be renumbered with a first line number of n and in line number steps of m. Both n and m must be present and if the renumbering would cause any line number to exceed 32767 then the original numbering is retained. Command: F n,m,f,s The text existing within the line range n < x < m is searched for an occurence of the string f - the 'find' string. If such an occurence is found then the relevant text line is displayed and the Edit mode is entered - see below. You may then use commands within the Edit mode to search for subsequent occurences of the string f within the defined line range or to substitute the string s (the 'substitute' string) for the current occurence of f and then search for the next occurence of f; see below for more details. - Page 23 --------------------------------------------------------------------- Note that the line range and the two strings may have been set up previously by any other command so that it may only be necessary to enter 'F' to initiate the search - see the example in Section 3.3 for clarification. Command: E n Edit the line with line number n. If n does not exist then no action is taken; otherwise the line is copied into a buffer and is displayed again underneath the line and the Edit mode is entered. All subsequent editing takes place within the buffer and not in the text itself; thus the original line can be recovered at any time. In this mode a pointer is imagined moving through the line (starting at the first character) and various sub-commands are supported which allow you to edit the line. The sub-commands are: ' ' (space) - increment the text pointer by one i.e. point to the next character in the line. You cannot step beyond the end of the line. CAPS SHIFT 0 - decrement the text pointer by one to point at the previous character in the line. You cannot step backwards beyond the first character in the line. CAPS SHIFT 8 - step the text pointer forwards to the next tab position on each screen line. ENTER - end the edit of this line keeping all the chanes made. Q - quit the edit of this line i.e. leave th edit ignoring all the changes made and leaving the line as it was before the edit was initiated. R - reload the edit buffer from the text i.e. forget all changes made on this line and restore the line as it was originally. L - list the rest of the line being edited i.e. the remainder of the line beyond the current pointer position. You remain in the Edit mode with the pointer re-positioned at the start of the line. K - kill (delete) the character at the current pointer position. Z - delete all the characters from (and including) the current pointer position to the end of the line. F - find the next occurence of the 'find' string previously defined within a command line (see the 'F' commmand above). This - Page 24 --------------------------------------------------------------------- sub-command will automaticall exit the edit on the current line (keeping the changes) if it does not find another occurence of the 'find' string in the current line. If an occurence of the 'find' string is detected in a subsequent line (within the previously specified line range) then the Edit mode will be entered for the line in which the string is found. Note that the text pointer is always positioned at the start of the found string. S - substitute the previously defined 'substitute' string for the currently found occurence of the 'find' string and then perform the sub-command 'F' i.e. search for the next occurence of the 'find' string. This, together with the above 'F' sub-command, is used to step through the textfile optionally replacing occurences of the 'find' string with the 'substitute' string - see Section 3.3 for an example. I - insert characters at the current pointer position. You will remain in this sub-mode until you press ENTER - this will return you to the main Edit mode with the pointer positioned after the last character inserted. Using CAPS SHIFT 0 (DELETE) within this sub-mode will cause the character to the left of the pointer to be deleted from the buffer while the use of CAPS SHIFT 8 will advance the pointer to the next tab position, inserting spaces. X - this advances the pointer to the end of the line and automatically enters the insert sub-mode detailed above. C - change sub-mode. This allows you to overwrite the character at the current pointer position and then advances the pointer by one. You remain in the change sub-mode until you press ENTER whence you are taken back to the Edit mode with the pointer positioned after the last character you changed. CAPS SHIFT 0 within this sub-mode simply decrements the pointer by one i.e. moves it left while CAPS SHIFT 8 has no effect. 3.2.4 Tape/Microdrive Commands Text may be saved to tape/microdrive or loaded from tape/microdrive using the commands 'P','G' and 'T'. Object code may be saved to tape/microdrive using the 'O' command. Command: P n,m,s The line range defined by n < x < m is saved to tape or microdrive under the filename specified by the string s. The text will be saved to microdrive if the filename begins with a drive number followed by a colon (':'). Remember that these arguments may have been set by a previous command. Examples: P10,200,EXAMPLE saves lines 10-200 to tape as EXAMPLE P500,900,1:TEST saves lines 500-900 to microdrive 1 - Page 25 --------------------------------------------------------------------- Before entering this command make sure that your tape recorder is switched on and in RECORD mode, if saving to tape. Do not use this command if you wish, at a later stage, to 'Include' the text from tape - use the 'T' command instead. If you intend to 'include' from microdrive then you should use this 'P' command. When 'P'utting to microdrive and the filename you have specified already exists on the cartridge, you will be asked: File Exists Delete (Y/N)? answer Y to delete the file and continue saving or any other key to return to the eitor without saving the file. Command: G,,s The tape or microdrive is searched for a file with a filename of s; when found, it is loaded at the end of the current text. If a null strin is specified as the filename then the first textfile on the tape is loaded. For microdrive, you must specify a filename and it should begin with a drive number followed by a colon. If using cassette, after you have entered the 'G' command, the message 'Start tape...' is displayed - you should now press PLAY on your recorder. A search is now made for a textfile with the specified filename, or the first textfile if a null filename is given. If a match is made then the message 'Using filename' is displayed, otherwise 'Found filename' is shown and the search of the tape continues. If using microdrive and the specified file cannot be found then the message 'Absent' is displayed. Note that if any textfile is already present in the memory then the textfile that is loaded from tape will be appended to the existing file and the whole file will be renumbered starting with line 1 in steps of 1. Command: T n,m,s Dump out a block of text, between the line numbers n and m inclusive, to tape in a format suitable for inclusion at a later stage via the assembler command *F - see Section 2.9. The file is dumped with the filename s. The dump takes place immediately you have pressed ENTER so you should ensure that your tape recorder is ready to record before entering this command line. If you intend to include from microdrive then use the 'P' command to save the text, as usual, and not this 'T' command. Note that this command is to be used only if you want to assemble the text from tape at a later stage. - Page 26 --------------------------------------------------------------------- Command: O,,s Dump out your object code to cassette or microdrive. The filename s can be up to 8 characters in length and should begin with a drive number (1-8) and a colon if you ish to save the object code to microdrive. Only the last 'block' of code produced by the assembler can be saved in this way i.e. if you have more than one ORG directive in your source program then only the code produced after the last ORG is saved. Code must have been produced in memory before it can be saved using 'O'. 3.2.5 Assembling and Running from the Editor. Command: A This causes the text to be assembled from the first line in the textfile. See Section 2 for further details. Command: R If the source has been assembled without errors and an execute address has been specified by the use of the ENT assembler directive then the 'R' command may b used to execute the object program. The object program can use a RET (#C9) instruction to return to the editor so long as the stack is in the same position at the end of the execution of the program as it was at the beginning. Note that ENT will have no effect if Option 16 has been specified for the assembly. Before entering the code, interrupts are enabled and register IY is loaded with the value #5C3A. 3.2.6 Other Commands. Command: B This simply returns control to the operating system. To re-enter the assembler use either a cold or a warm start - see Section 1. Command: C This allows you to configure the size of the Include and Macro buffers. The include buffer is the buffer in which text is held when assembling directly from cassette or Microdrive - the larger this - Page 27 --------------------------------------------------------------------- buffer, the more text that will be read in from cassette or microdrive at one go and therefore the faster the assembly will proceed. On the other hand, more memory is used. Thus, there is a compromise to be made between speed of assembly and use of memory; the 'C' command allows you to control this tradeoff by giving you the opportunity of setting the size of the Include buffer. The Macro buffer is used to hold the text of any macro definitions that you may use. The 'C' command prompts you to enter the 'Include buffer' size and then the 'Macro buffer' size. In both cases simply enter the number of bytes (in decimal) that you wish to allocate, followed by ENTER. If you press ENTER by itself without entering a number then no action is taken. If you specify an Include buffer size then the size is forced to be a minimum of 256 bytes. You may abort the command using CAPS SHIFT 1. Please note that 'C' effectively performs a cold start on your text, deleting it. Thus, remember to save any existing text before using the 'C' command. It is best to allocate the buffers as large as you will need them at the start of a session. Command: Q This command allows you to convert textfiles produced by GENS1 to the compressed text format of GENS3. Simply lod up the GENS1 textfile, using the 'G' command, use the 'Q' command to convert the file and then dump the compressed file out using the 'P' command. 'Q' takes no arguments and may take a substantial time to complete the conversion of the file. Command: S,,d This command allos you to change the delimiter which is taken as separating the arguments in the command line. On entry to the editor the comma ',' is taken as the delimiter; this may be changed by the use of the 'S' command to the first character of the specified string d. Remember that once you have defined a new delimiter it must be used (even within the 'S' command) until another one is specified. Please do not confuse this command with the 'S'ubstitute sub-command within edit mode. Note that the separater may not be a space. Command: V The 'V' command displays the current values of N1, N2, S1 and S2 plus the current command delimiter i.e. the two default line numbers, the default strings and the delimiter. This is useful - Page 28 --------------------------------------------------------------------- before entering any command in which you are going to use default values, to check that these values are corect. Command: W n,m The 'W' command causes the section of text between lines n and m inclusive to be output to the printer. If both n and m are defaulted then the whole textfile will be printed. The printing will pause after the number of lines set by the 'K' command - press any key to continue printing. Command: X 'X' simply causes the start and end address of the textfile to be displayed in decimal. This is useful if you wish to save the text from within BASIC, or if you want to see how much memory you have left after the textfile. GENS3 always expects the text to start at the first address given by the 'X' command and holds the end address of the text in location TEXTEND which is at 'Start of GENS3 + 54'. Thus, if you wish to 'patch in' a textfile (perhaps produced by MONS3) you must move the textfile to the address specified by the first address displayed by the 'X' command, modify TEXTEND to contain the end address of the file and finally enter GENS3 via a warm start. For example, say you have generated a textfile in the correct place and that it ends (the address after the final end-of-line marker) at #9A02. Then, assuming that you have loaded GENS3 at 24064, you should, from BASIC, POKE 24064+54,2 (#02) and POKE 24064+55,154 (#9A) and then enter GENS3 by RANDOMIZE USR 24125. You will now be able to work with the textfile normally from within the editor. Command: H,,s Allows you to verify a textfile that has been saved to microdrive. Simply use H,,n:filename where n is the drive number and filename is the name you gave to the textfile on that drive. The file will be opened and each record in turn inspected to make sure that it can be read from the drive; record numbers are displayed as they are checked. If a particular record number fails the check then 'File not found' will be displayed and control returned to BASIC. If verification is successful then control will be returned to the assembler's editor. 3.3 An Example of the Use of the Editor. ---------------------------------------- Let us assume that you have typed in the following program (using I10,10): - Page 29 --------------------------------------------------------------------- 10 *h 16 BIT RANDOM NUMBERS 20 30 ;INPUT: HL contains previous random number or seed. 40 ;OUTPUT: HL contains new randon number 50 60 Random PUSH AF ;save registers 70 PUSH BC 80 PUSH HL 90 ADD HL,HL ;*2 100 ADD HL,HL ;*4 110 ADD HL,HL ;*8 120 ADD HL,HL ;*16 130 ADD HL,HL ;*32 140 ADD HL,HL ;*64 150 PIP BC ;old random number 160 ADD HL,DE 170 LD DE,41 180 ADD HL,DE 190 POP BC ;restore registers 200 POP AF 210 REY This program has a number of errors which are as follows: Line 10: a lower case 'h' has been used in the assambler command *H. Line 40: 'randon' instead of 'random'. Line 70: PUSH BC starts in the label field. Line 150: 'PIP' instead of 'POP'. Line 160: needs a comment (not an error - merely style). Line 210: 'REY' should be 'RET'. Also 2 extra lines of ADD HL,HL should be added between lines 140 and 150 and all references to the register pair DE in lines 160 to 180 should be to register pair BC. To put all this right we can proceed as follows: E10 ENTER then _(space) C(enter change mode) H ENTER ENTER F40,40,randon,random ENTER then the 'S' sub-command. E70 ENTER then I(insert mode) _______(7 spaces) ENTER ENTER I142,2 ENTER 142 _______ADD HL,HL ;*128 144 _______ADD HL,HL ;*256 CAPS SHIFT 1 F150,150,PIP,POP ENTER then the 'S' sub-command. E160 ENTER then X __ ;*257 + 41 ENTER ENTER F160,180,DE,BC ENTER then repated use of the sub-command 'S'. E210 ENTER C (change mode) T ENTER ENTER N10,10 ENTER to renumber the text. You are strongly recommended to work through the above example actually using the editor. - Page 30 --------------------------------------------------------------------- (blank page) - Page 31 --------------------------------------------------------------------- APPENDIX 1 ERROR NUMBERS AND THEIR MEANINGS. *ERROR* 1 Error in the context of this line. *ERROR* 2 Mnemonic not recognised. *ERROR* 3 Statement badly formed. *ERROR* 4 Symbol defined more than once. *ERROR* 5 Line contains an illegal character i.e. one which is not valid in a particular contet. *ERROR* 6 One of the operands in this line is illegal. *ERROR* 7 A symbol in this line is a reserved word. *ERROR* 8 Mismatch of registers. *ERROR* 9 Too many registers in this line *ERROR* 10 An expression that should evaluate to 8 bits evaluates to more than 8 bits. *ERROR* 11 The instructions JP (IX+n) and JP (IY+n) are illegal. *ERROR* 12 Error in the formation of an assembler directive. *ERROR* 13 Illegal forward reference i.e. an EQUate has been made to a symbol which has not yet been defined. *ERROR* 14 Division by zero. *ERROR* 15 Overflow in a multiplication operation. *ERROR* 16 Nested macro definition. *ERROR* 17 This identifier is not a macro. *ERROR* 18 Nested macro call. *ERROR* 19 Nested conditional statement. Bad ORG! An ORG has been made to an address that would corrupt GENS, its textfile or the symbol table. Control returns to the editor. Out of Table Space! Occurs during the first pass if insufficient memory has been allowed for the symbol table. Control returns immediately to the editor. Bad Memory! No room for any more text to be inserted i.e. the end of text is near the top of RAM. You should save the current textfile or part of it. - Page 32 --------------------------------------------------------------------- APPENDIX 2 RESERVED WORDS, MNEMONICS ETC. The following is a list of the reserved words within GENS. These symbols may not be used as labels although they may form part of a label. Note that all the reserved words are composed of capital letters. A B C D E H L I R $ AF AF' BC DE HL IX IY SP NC Z NZ M P PE PO There now follows a list of the valid Z80 mnemonics, assembler directives and assembler commands. Note that these also must be entered in capital letters. ADC ADD AND BIT CALL CCF CP CPD CPDR CPI CPIR CPL DAA DEC DI DJNZ EI EX EXX HALT IM IN INC IND INDR INI INIR JP JR LD LDD LDDR LDI LDIR NEG NOP OR OTDR OTIR OUT OUTD OUTI POP PUSH RES RET RETI RETN RL RLA RLC RLCA RLD RR RRA RRC RRCA RRD RST SBC SCF SET SLA SRA SRL SUB XOR DEFB DEFM DEFS DEFW ELSE END ENT EQU IF ORG MAC ENDM *D *E *H *L *S *C *F *M - Page 33 --------------------------------------------------------------------- APPENDIX 3 A WORKED EXAMPLE. There follows an example of a typical session using GENS3 - if you are a newcomer to the world of assembler programs or if you are simply a little unsure how to use the editor/assembler then we urge you to work through this example carefully. Note that is used to indicate that you should press ENTER on the keyboard. Session objective: To write and test a fast integer multiply routine, the text of which is to be saved to tape using the editor's 'T' command so that it can easily be 'included' from tape in future programs. Session workplan: 1. Write the multiply routine as a subroutine and save it to tape using the editor's 'P' command so that it can be easily retrieved and edited during this sessions, should bugs be present. 2. De-bug the multiply subroutine, editing as necessary. 3. Save the de-bugged routine to tape, using the editor's 'T' command so that the routine may be 'included' from tape in other programs. Before we start we must load GENS3 into the computer - do this by typing LOAD"" CODE 26000 ENTER to load the assembler at address 26000. Now type RANDOMIZE USR 26000 ENTER. You will now be prompted with a '>' sign - you are in editor mode ready to create assembly programs. Stage 1 - write the integer multiply routine. We use the editor's 'I' command to insert the text using CAPS SHIFT 8 (the tab character) to obtain a tabulated listing. We do not need to use CAPS SHIFT 8, a list of the text will always perform the tabulation for us. We have not indicated where tabs have been used below but you can assume that they are used before the mnemonic and between the mnemonic and the operand. Note that the addresses shown in the example assembler listings that follow may not correspond to those produced on your machine; they serve an illustrative purpose only. - Page 34 --------------------------------------------------------------------- >I10,10 10 ; A fast integer multiply 20 ; routine. Multiplies HL 30 ; by DE. Return the result 40 ; in HL. C flag set on an 50 ; overflow. 60 70 ; ORG #7F00 80 90 Mult OR A 100 SBC HL,DE ;HL>DE? 110 ADD HL,DE 120 JR NC,Mu1 ;yes 130 EX DE,HL 140 Mu1 OR D 150 SCF ;overflow if 160 RET NZ ;DE>255 170 OR E ;times 0? 180 LD E,D 190 JR NZ,MU4 ;no 200 EX DE,HL ;0 210 RET 220 230 ;Main routine. 240 250 Mu2 EX DE,HL 260 ADD HL,DE 270 EX DE,HL 280 Mu3 ADD HL,HL 290 RET C ;overflow 300 Mu4 RRA 310 JR NC,Mu3 320 OR A 330 JR NZ,Mu2 340 ADD HL,DE 350 RET 360 CAPS SHIFT 1 >P10,350,Mult > The above will create the text of the routine and save it to tape. Remember to have your tape recorder running and in RECORD mode before issuing the 'P' command. Stage 2 - de-bug the routine. First, let's see if the text assembles correctly. We will use option 6 so that no listing is produced and no object code generated. >A Table size: {default the symbol table size} Options: 6 - Page 35 --------------------------------------------------------------------- *HISOFT GENS3 ASSEMBLER* Copyright Hisoft 1983,84 All Rights Reserved Pass 1 errors: 00 Pass 2 errors: 00 *WARNING* MU4 absent Table used: 74 from 161 > We see from this assembly that we have made a mistake in line 190 and entered MU4 instead of Mu4 which is the lbel we wish to branch to. So edit line 190: >F190,190,MU4,Mu4 190 JR NZ, {now use the 'S' sub-command} > Now assemble the text again and you should find that it assembles without errors. So now we must write some code to test the routine: >N300,10 {renumber so that we can write some more text} >I10,10 10 ;Some code to test 20 ;the Mult routine. 30 40 LD HL,50 50 LD DE,20 60 CALL Mult ;Multiply 70 LD A,H ;o/p result 80 CALL Aout 90 LD A,L 100 CALL Aout 110 RET ;Return to editor 120 130 ;Routine to o/p A in hex 140 150 Aout PUSH AF 160 RRCA 170 RRCA 180 RRCA 190 RECA 200 CALL Nibble 210 POP AF 220 Nibble AND %1111 230 ADD A,#90 240 DAA 250 ADC A,#40 260 DAA 270 LD IY,#5C3A ; for ROM - Page 36 --------------------------------------------------------------------- 280 RST #10 ; ROM call 290 RET 300 CAPS SHIFT 1 > Now assemble the test routine and the Mult routine together. >A Table size: Options: 6 *HISOFT GENS3 ASSEMBLER* Copyright HISOFT 1983,84 All rights reserved 7EAC 190 RECA *ERROR* 02 {hit any key to continue} Pass 1 errors: 01 Table used: 88 from 210 > We have an error in our routine; RECA should be RRCA in line 190. So: >E190 190 RECA 190 _______C {enter change mode} R Now assemble again, using simply option 4 (no list), and then the text should assemble correctly. Assuming it does, we are now in a position to test the working of our Mult routine so we need to tell the editor where it can execute the code from. We do this with the ENT directive: >35 ENT $ Now assemble the text again and the assembly should terminate correctly with the messages: Table used: 88 from 211 Executes: 32416 > or something similar. Now we can run our code using the editor's 'R' command. We should expect it to multiply 50 by 20 producing 1000 which is #3E( in hexadecimal. >R 0032> - Page 37 --------------------------------------------------------------------- It doesn'nt work! Why not? List the lines 380 to 500 (L380,500). You will see that at line 430 the instruction is an OR D followed, effectively, by a RET NZ. What this is doing is a logical OR between the D register and the accumulator A and returning with an error flag set (the C flag) if the result is non-zero. The object of this is to ensure that DE<256 so that the multiplication does not overflow - it does this by checking that D is zero ... but the OR will only work correctly in this case if the accumulator A is zero to start with, and we have no guarantee that this is so. We must ensure that A is zero before doing the OR D, otherwise we will get unpredictable overflow with the higher number returned as the result. From inspection of the code we see that the OR A at line 380 could be made into a XOR A thus setting the flags for the SBC HL,DE instruction and setting A to zero. So: >E380 380 Mult OR A 380 ________I {enter insert mode}X Now assemble again (option 4) and run the code, using 'R'. The answer should now be correct - #3E8. We can further check the routine by editing lines 40 and 50 to multiply different numbers and then assembling and running - you should find that the routine works perfectly. Now we have perfected the routine we can save it to tape in 'Include' format: >T300,999,Mult Remember to start the recorder in RECORD mode before pressing ENTER. Once the routine has been saved like this it may be included in a program as shown below: 500 RET 510 520 ;Include the Mult routine here 530 540 *F Mult 550 560 ;The next routine. When the above text is assembled the assembler will ask you to 'Start tape...' when it gets to line 540 on both th first and second pass. Therefore you should have the Mult dump cued up on the tape in both cases. This will normally mean rewinding the tape after the first pass. You could record two dumps of Mult on the tape, following each other and use one for the first pass and the other for the second pass. Please study the above example carefully and try it out for yourself. - Page 38 --------------------------------------------------------------------- (blank page) - Page 39 --------------------------------------------------------------------- APPENDIX 4 AN EXTENDED CAT PROGRAM We present below an assembly listing of a program that produces a CATalogue of a Microdrive cartridge similar to that produced by ZX BASIC'S CAT command but with extra information viz. Type of file: D - a data or print-type file P - a BASIC program file B - a CODE file S - a string array N - a numeric array Also, for a CODE file, the length and start address are displayed in decimal while, for a program file, the length and autoexecution address are displayed in decimal. To use the program either type in the hex codes directly (using MONS3 or POKE from BASIC) or use GENS3 to assemble the source of the program. Note that the program is positioned at 60000 - you may of course change this and re-assemble. Once the code is in the Spectrum's memory you may execute it from within BASIC or path it into the GENS3 editor. To use the program from within BASIC, first POKE the Microdrive number that you wish to catalogue into location 60345 (assuming that the code starts at 60000) and then RANDOMIZE USR 60000. To use the catalogue program from within GENS3 you must patch the dummy 'Z' command to jump to the CATalogue code. To do this patch, load up GENS3 normally and then POKE the address of the extended CATalogue routine + 2 into locations Start of GENS3 + 7790 and Start of GENS3 + 7791 (low order byte first). For example, say you have loaded GENS3 at 26000 and the extended CATalogue routine is at 60000. Then to effect the patch simply POKE 33790,98 and POKE 33791,234 and then enter GENS3 in the normal way. You can then use Zn from within the editor to CATalogue drive number n. Below is the listing of the extended CATalogue program: - Page 40 --------------------------------------------------------------------- Microdrive Extended CATalogue 28 February 1984 1 *H Microdrive Extended CATalogue 28 February 1984 2 *C+ 3 ;Produced with Hisoft's GEN assembler 4 5 ;Copyright Hisoft 1984 6 ;With many thanks to Andre Pennell for his 7 ;Microdrive 'bible'and the Stream 14 routine 8 9 ;Equates 10 000D 11 CR EQU 13 12 0002 13 PRINT EQU 2 0043 14 RECFLG EQU 67 15 15D4 16 WAIT_K EQU #15D4 1655 17 MAKE_S EQU #1655 18 5C16 19 STRMS EQU #5C16 5C3A 20 ERR_NR EQU #5C3A 5C4F 21 CHANS EQU #5C4F 5C53 22 PROG EQU #5C53 23 5CD6 24 D_STR1 EQU #5CD6 5CD8 25 S_STR1 EQU #5CD8 5CDA 26 N_STR1 EQU #5CDA 5CDC 27 T_STR1 EQU #5CDC 5CE6 28 HD_00 EQU #5CE6 5CE7 29 HD_0B EQU #5CE7 5CE9 30 HD_0D EQU #5CE9 5CEB 31 HD_0F EQU #5CEB 5CED 32 HD_11 EQU #5CED 33 0022 34 OPEN_M EQU #22 0023 35 CLOSE_ EQU #23 0031 36 NEWVAR EQU #31 0032 37 SHADOW EQU #32 38 39 ;For GENS3M2 only. 40 1C81 41 NUM1of EQU 7297 42 43 EA60 44 ORG 60000 45 46 ;BASIC entry point 47 EA60 1817 48 JR BasEnt 49 50 ;GENS3M2 entry point 51 EA62 E1 52 POP HL EA63 54 53 LD D,H EA64 5D 54 LD E,L EA65 E5 55 PUSH HL EA66 21811C 56 LD HL,NUM 1off EA69 19 57 ADD HL,DE EA6A 7E 58 LD A,(HL) EA6B 23 59 INC HL EA6C B6 60 OR (HL) EA6D 2002 61 JR NZ,NumSet EA6F 3E01 62 LD A,1 EA71 E60F 63 NumSet AND %00001111 EA73 2600 64 LD H,0 EA75 6F 65 LD L,A EA76 22B9EB 66 LD (DRIVE),HL 67 68 ;Initialise 69 EA79 210AEC 70 BasEnt LD HL,SPACE EA7C 2208EC 71 LD (POINTER),HL EA7F FD213A5C 72 LD IY,#5C3A 73 EA83 21C5EB 74 LD HL,SIGNON EA86 0634 75 LD B,SIGNEND-SIGNON EA88 CD9AEB 76 CALL WRstring 77 78 ;Set upnew channel and attach to Stream 14 79 EA8B 2A535C 80 LD HL,(PROG) EA8E 2B 81 DEC HL EA8F E5 82 PUSH HL EA90 010B00 83 LD BC,11 EA93 CD5516 84 CALL MAKE_SPACE EA96 2191EB 85 LD HL,CH14out EA99 D1 86 POP DE EA9A D5 87 PUSH DE EA9B EB 88 EX DE,HL EA9C 73 89 LD (HL),E EA9D 23 90 INC HL EA9E 72 91 LD (HL),D EA9F 23 92 INC HL EAA0 EB 93 EX DE,HL EAA1 21FDEB 94 LD HL,C14INFO EAA4 010900 95 LD BC,11-2 EAA7 EDB0 96 LDIR EAA9 E1 97 POP HL EAAA 23 98 INC HL EAAB ED4B4F5C 99 LD BC,(CHANS) EAAF B7 100 OR A EAB0 ED42 101 SBC HL,BC EAB2 22325C 102 LD (STRMS+28),HL 103 104 ;Now read in bare catalogue 105 EAB5 D9 106 EXX EAB6 E5 107 PUSH HL EAB7 D9 108 EXX 109 EAB8 CF 110 RST 8 EAB9 31 111 DEFB NEWVARS 112 - Page 41 --------------------------------------------------------------------- EABA 3E0E 113 LD A,14 EABC 32D85C 114 LD (S_STR1),A EABF 2AB9EB 115 LD HL,(DRIVE) EAC2 22D65C 116 LD (D_STR1),HL EAC5 2A06EC 117 LD HL,(CAT) EAC8 22ED5C 118 LD (HD_11),HL EACB FB 119 EI EACC CF 120 RST 8 EACD 32 121 DEFB SHADOW 122 123 ;Now process bare catalogue 124 EACE 210AEC 125 LD HL,SPACE EAD1 060B 126 LD B,11 EAD3 CD9AEB 127 CALL WRstring EAD6 060F 128 CatL1 LD B,15 EAD8 C5 129 CatLoo PUSH BC EAD9 23 130 INC HL EADA 7E 131 LD A,(HL) EADB FE0D 132 CP CR ;finished? EADD 2879 133 JR Z,CatEnd EADF 2B 134 DEC HL EAE0 060B 135 LD B,11 EAE2 E5 136 PUSH HL EAE3 CD9AEB 137 CALL WRstring EAE6 E3 138 EX (SP),HL EAE7 23 139 INC HL EAE8 EB 140 EX DE,HL EAE9 21DC5C 141 LD HL,T_STR1 EAEC 73 142 LD (HL),E EAED 23 143 INC HL EAEE 72 144 LD (HL),D EAEF 2AB9EB 145 LD HL,(DRIVE) EAF2 22D65C 146 LD (D_STR1),HL EAF5 210A00 147 LD HL,10 EAF8 22DA5C 148 LD (N_STR1),HL EAFB FB 149 EI EAFC CF 150 RST 8 EAFD 22 151 DEFB OPEN_M EAFE CDB5EB 152 CALL Space EB01 DDCB4356 153 BIT PRINT,(IX+RECFLG) EB05 2007 154 JR NZ,NotPrint EB07 3E44 155 LD A,"D" EB09 CDACEB 156 CALL CONOUT EB0C 1841 157 JR CatBack EB0E DDE5 158 NotPri PUSH IX EB10 D1 159 POP DE EB11 215200 160 LD HL,82 EB14 19 161 ADD HL,DE EB15 EB 162 EX DE,HL EB16 1A 163 LD A,(DE) EB17 13 164 INC DE EB18 21F9EB 165 LD HL,TYPETAB EB1B 4F 166 LD C,A EB1C 0600 167 LD B,0 EB1E 09 168 ADD HL,BC EB1F 7E 169 LD A,(HL) EB20 CDACEB 170 CALL CONOUT EB23 CDB5EB 171 CALL Space EB26 EB 172 EX DE,HL EB27 79 173 LD A,C EB28 B7 174 OR A EB29 2013 175 JR NZ,NotProg EB2B 23 176 INC HL EB2C 23 177 INC HL EB2D 23 178 INC HL EB2E 23 179 INC HL EB2F 5E 180 LD E,(HL) EB30 23 181 INC HL EB31 56 182 LD D,(HL) EB32 23 183 INC HL EB33 CD66EB 184 CALL DEOUTS EB36 5E 185 LD E,(HL) EB37 23 186 INC HL EB38 56 187 LD D,(HL) EB39 CD66EB 188 CALL DEOUTS EB3C 1811 189 JR CatBack EB3E FE03 190 NotPro CP 3 EB40 200D 191 JR NZ,CatBack EB42 5E 192 LD E,(HL) EB43 23 193 INC HL EB44 56 194 LD D,(HL) EB45 23 195 INC HL EB46 CD66EB 196 CALL DEOUTS EB49 5E 197 LD E,(HL) EB4A 23 198 INC HL EB4B 56 199 LD D,(HL) EB4C CD66EB 200 CALL DEOUTS EB4F CF 201 CatBac RST 8 EB50 23 202 DEFB CLOSE_M EB51 E1 203 POP HL EB52 C1 204 POP BC EB53 1083 205 DJNZ CatLoop EB55 C3D6EA 206 JP CatL1 207 EB58 C1 208 CatEnd POP BC EB59 2B 209 DEC HL EB5A 0605 210 LD B,5 EB5C CD9AEB 211 CALL WRstring EB5F D9 212 EXX EB60 E1 213 POP HL EB61 D9 214 EXX EB62 010000 215 LD BC,0 EB65 C9 216 RET 217 218 ;OutputDE in decimal 219 EB66 E5 220 DEOUTS PUSH HL EB67 DDE5 221 PUSH IX EB69 EB 222 EX DE,HL EB6A 0605 223 LD B,5 EB6C DD21BBEB 224 LD IX,TENTAB EB70 DD5E00 225 DEloop LD E,(IX) EB73 DD5601 226 LD D,(IX+1) EB76 3EFF 227 LD A,-1 EB78 3C 228 TenLoo INC A - Page 42 --------------------------------------------------------------------- EB79 B7 229 OR A EB7A ED52 230 SBC HL,DE EB7C 30FA 231 JR NC,TenLoop EB7E 19 232 ADD HL,DE EB7F F630 233 OR #30 EB81 CDACEB 234 CALL CONOUT EB84 DD23 235 INC IX EB86 DD23 236 INC IX EB88 10E6 237 DJNZ DEloop EB8A CDB5EB 238 CALL Space EB8D DDE1 239 POP IX EB8F E1 240 POP HL EB90 C9 241 RET 242 243 ;Outputfor Stream14 244 EB91 2A08EC 245 CH14ou LD HL,(POINTER) EB94 77 246 LD (HL),A EB95 23 247 INC HL EB96 2208EC 248 LD (POINTER),HL EB99 C9 249 RET 250 251 ;Writea string oflength B from (HL) 252 EB9A 7E 253 WRstri LD A,(HL) EB9B CDACEB 254 CALL CONOUT EB9E 23 255 INC HL EB9F 10F9 256 DJNZ WRstring EBA1 C9 257 RET 258 259 ;Open a stream 260 EBA2 E5 261 ChOpen PUSH HL EBA3 D5 262 PUSH DE EBA4 C5 263 PUSH BC EBA5 CD0116 264 CALL #1601 EBA8 C1 265 POP BC EBA9 D1 266 POP DE EBAA E1 267 POP HL EBAB C9 268 RET 269 270 ;Output to stream 2 271 EBAC F5 272 CONOUT PUSH AF EBAD 3E02 273 LD A,2 EBAF CDA2EB 274 CALL ChOpen EBB2 F1 275 POP AF EBB3 D7 276 RST #10 EBB4 C9 277 RET 278 279 ;Output a space to stream 2 280 EBB5 3E20 281 Space LD A," " EBB7 18F3 282 JR CONOUT 283 284 285 ;Storage 286 EBB9 0100 287 DRIVE DEFW 1 288 EBBB 1027E803 289 TENTAB DEFW 10000,1000,100,10,1 290 EBC5 0D 291 SIGNON DEFB CR EBC6 4869736F 292 DEFM "Hisoft Extended CAT Listing" EBE1 0D 293 DEFB CR EBE2 436F7079 294 DEFM "Copyright Hisoft 1984" EBF7 0D0D 295 DEFB CR,CR EBF9 296 SIGNEN EQU $ 297 EBF9 504E5342 298 TYPETA DEFM "PNSB" 299 EBFD C415 300 C14INF DEFW #15C4 EBFF 5A 301 DEFB "Z" EC00 28002800 302 DEFW #28,#28,11 303 304 ;*** this value may change with new Interface 1 ROM*** 305 EC06 581C 306 CAT DEFW #1C58 *) 307 308 ;***************************************************** 309 EC08 310 POINTE DEFS 2 EC0A 311 SPACE DEFS 512 312 Pass 2 errors: 00 *) 2nd issue #1C52 *) 3rd issue #1C54 - Page 43 --------------------------------------------------------------------- H i S o f t M O N S 3 Programmer's Manual - Page 44 --------------------------------------------------------------------- (blank page) - Page 45 --------------------------------------------------------------------- SECTION 1 GETTING STARTED MONS3 is supplied in a relocatable form; you simply load it iat the address that you wish it to execute from and then enter MONS3 via that address. If you wish to enter MONS3 again (having returned from MONS3 to BASIC) then you should execute the address at which you originally loaded the debugger. Example: Say you want to load MONS3 at address #C000 (49152 decimal) - proceed as follows: LOAD "MONS3" CODE 49152 RANDOMIZE USR 49152 To enter MONS3 again use: RANDOMIZE USR 49152 MONS3 is roughly 5K in length once it has been relocated but you should allow nearer 6K bytes on loading MONS3 owing to the table of relocation addresses which comes after the main code. MONS3 contains its own internal stack so that it is a self-contained programs. Making a Backup Copy. Once you have loaded MONS3 into your Spectrum's memory then you can make a backup copy of the package as follows: SAVE "MONS3" CODE xxxxx,6068 to cassette SAVE *"M";1;"MONS3" CODE xxxxx,6068 to Microdrive where: xxxxx is the address at which you loade MONS3. Please note that we allow you to make a backup copy of MONS3 for your own use so that you can program with confidence. Please do not copy MONS3 to give (or worse, sell) to your friends, we supply very reasonably priced software and a full after-sales support service but if enough people copy our software we shall not be able to continue this; please buy, don't steal. Once you have entered MONS3 the message '*MONS3 (C) Copyright 1983*' will appear for a few seconds to be replaced by a 'front panel' display (see the Appendix for an example display). This consist of the Z80 registers and flags together with their contents plus a 24 byte section of memory centred (using '>' and '<') around the current value of the Memory Pointer which is initially set to address 0. On the top line of the display is a dis-assembly of the instruction addressed by the Memory Pointer. - Page 46 --------------------------------------------------------------------- On entry to MONS3, all the addresses displayed within the Front Panel are given in hexadecimal format (i.e. to base 16); you can change this so that the addresses are shwon in decimal by using the command SYMBOL SHIFT 3 - see then next section. Note, however, that addresses must always be entered in hexadecimal. Commands are entered from the keyboard in response to the prompt '>' under the memory display and may be entered in upper or lower case. Some commands, whose effect might be disastrous if used in error, require you to press SYMBOL SHIFT as well as the command letter. Throughout this manual the use of the SYMBOL SHIFT key may be represented by the symbol '^' e.g. ^Z means hold the SYMBOL SHIFT and Z key down together. Comamnds take effect immediately - there is no need to terminate them with . Invalid commands are simply ignored. The entire 'front panel' display is updated after each command is processed so that you can observe any results of the particular command. Many commands require the input of a hexadecimal number - when entering a hexadecimal number you may enter as many hexadecimal digits (0-9 and A-F or a-f) as you wish and terminate them with any non-hex digit. If the terminator is a valid command then the command is obeyed after any previous command has been processed. If the terminator is a minus sign '-' then the negative of the hexadecimal numberr entered is returned - in two's complement form e.g. 1800- gives E800. If you enter more than 4 digits when typing a hexadecimal number then only the last 4 typed are retained and displayed on the screen. If, at any stage, you wish to return to the BASIC interpreter from MONS then simply press CAPS SHIFT 1 IMPORTANT NOTE: MONS3 disables interrupts in order to ensure correct functioning - the user should ensure that interrupts are not re-enabled during a session with MONS3. - Page 47 --------------------------------------------------------------------- SECTION 2 THE COMMANDS AVAILABLE. The following commands are available from within MONS3. In this section, whenever ENTER is used to terminate a hexadecimal number this in fact can be any non-hex character (see Section 1). Also '_' is used to denote a space where applicable. SYMBOL SHIFT 3 flip the number base in which addresses are displayed between base 16 (hexadecimal) nd base 10 (denary). On entry to MONS3, addresses are shown in hexadecimal, use ^3 to flip to a decimal display and ^3 again to revert to the hexadecimal format. This affects all addresses displayed by MONS3 including those generated by the dis-assembler but it does not change the display of memory contents - this is always given in hexadecimal. SYMBOL SHIFT 4 or '$' display a page of dis-assembly starting from the address held in the Memory Pointer. Useful to look ahead on your current position to see what instructions are coming up. Hit ^4 again to return to the 'Front Panel' display or another key to get a further page of dis-assembly. ENTER increment the Memory Pointer by one so that the 24 byte memory display is now centred around an address one greater than it was previously. CAPS SHIFT 7 decrement the Memory Pointer by one. CAPS SHIFT 5 decrement the Memory Pointer by eight - used to step backwards quickly. CAPS SHIFT 8 increment the Memory Pointer by eight - used to step forwards quickly. ',' (comma) update the Memory Pointer so that it contains the address currently on the stack (indicated by SP). This is useful when you want to look around the return address of a called routine etc. - Page 48 --------------------------------------------------------------------- 'G' search memory for a specified string ('G'et a string). You are prompted with a ':' and you should then enter the first byte for which you want to search followed by 'ENTER' - now keep entering subsequent bytes (and 'ENTER') in response to the ':' until you have defined the whole string. Then just press 'ENTER' in response to the ':', this will terminate the definition of the string and search memory, starting from the current Memory Pointer address, for the first occurence of the specified string. When the string is found the 'front panel' display will be updated so that the Memory Pointer is positioned at the first character of the string. Example: Say that you wish to search memory, starting from #8000, for occurences of the pattern #3E #FF (2 bytes) - proceed as follows; M:8000 ENTER set the Memory Pointer to #8000 G:3E ENTER define the first byte of the string. FF ENTER define the second byte of the string. ENTER terminate the string. After the final ENTER (or any non-hex character) 'G' proceeds to search memory from #8000 for the first occurence of #3E #FF. When found the display is updated - to find subsequent occurences of the string use 'N' command. 'H' convert a decimal number to its hexadecimal equivalent. You are prompted with ':' to enter a decimal number terminated by any non-digit (i.e. any character other than 0..9 inclusive). Once the number has been terminated, an '=' sign is displayed on the same line followed by the hexadecimal equivalent of the decimal number. Now hit any key to return to the command mode. Example: H:41472_=A200 here a space was used as the terminator. 'I' intelligent copy. This is used to copy a block of memory from one location to another - it is intelligent in that the block of memory may be copied to locations where it would overlap its previous locations. - Page 49 --------------------------------------------------------------------- 'I' prompts for the inclusive start and end addresses of the block to be copied ('First:', 'Last:') and then for the address to which the block is to be moved ('To:'); enter hexadecimal numbers in response to each of these prompts. If the start address is greater than the end address then the command is aborted - otherwise the block is moved as directed. 'J' execute code from a specified address. This command prompts, via ':', for a hexadecimal number - once this is entered the internal stack is reset, the screen cleared and execution transferred to the specified address. If you wish to return to the 'front panel' after executing code then set a breakpoint (see the 'W' command) at the point where you wish to return to the display. Example: J:B000 ENTER executes the code starting at #B000 You may abort this command before you terminate the address by using CAPS SHIFT 5. Note that 'J' corrupts the Z80 registers before executing the code; thus the machine program should make no assumptions as to the values held in the registers. If you wish to execute code with the registers set to particular values then you should use the SYMBOL SHIFT K command - see below. 'SYMBOL SHIFT K' continue execution from the address currently held in the Program Counter (PC). This command will probably be used most frequently in conjunction with the 'W' command - an example should help to clarify this usage: say you are single-stepping (using '^Z') through the code given below and you have reached address #8920. You are now not interested in stepping through the subroutine at #9000 but wish to see how the flags are set up after the call to the subroutine at #8800. 891E 3EFF LD A,-1 8920 CD0090 CALL #9000 8923 2A0080 LD HL,(#8000) 8926 7E LD A,(HL) 8927 111488 LD DE,#8814 892A CD0088 CALL #8800 892D 2003 JR NZ,labl 892F 320280 LD (#8002),A 8932 211488 labl LD HL,#8814 - Page 50 --------------------------------------------------------------------- Proceed as follows: set a breakpoint, using 'W', at location #892D (remember to use 'M' first to set the Memory Pointer) and then issue a '^K' command. Execution continues from the address held in the PC which, in this case, is #8920. Execution will then continue until the address at which the breakpoint was set (#892D) at which point the display will be updated and you can inspect the state of flags etc. after the call to the subroutine at #8800. Then you can resume single-stepping through the code. So '^K' is useful for executing code without first resetting the stack or corrupting the registers as 'J' does. 'L' tabulate, or list, a block of memory starting from the address currently held in the Memory Pointer. 'L' clears the screen and displays the hexadecimal representation and ASCII equivalence of the 80 bytes of memory starting from the current value of the Memory Pointer. Addresses will be shown in either hexadecimal or decimal depending on the current state of the Front Panel (see ^3 above). The display consists of 20 rows with 4 bytes per row, the ASCII being shown at the end of each row. For the purposes of the ASCII display any values above 127 are decremented by 128 and any values between 0 an 31 inclusive are shown as '.'. At the end of a page of the list you have the option of returning to the main 'front panel' display by pressing CAPS SHIFT 5 or continuing with the next page of 80 bytes by pressing any other key (other than CAPS SHIFT 1). 'M' set the Memory Pointer to a specified address. You are prompted with ':' to enter a hexadecimal address (see Section 1). The Memory Pointer is then updated with the address entered and the memory display of the 'front panel' changes accordingly. M is useful as a prelude to entering code, tabulating memory etc. 'N' find the next occurence of the hex string last specified by the 'G' command. 'G' allows you to define a string and then searches for the first occurence of it; if you want further occurences of the string then use 'N'. - Page 51 --------------------------------------------------------------------- 'N' begins searching from the Memory Pointer and updates the memory display when the next occurence of the string is found. 'O' go to the destination of a relative displacement. The command takes the byte currently addressed by the Memory Pointer, treats it as a relative displacement and updates the memory display accordingly. Example: Say the Memory Pointer is set to #6800 and that the contents of locations #67FF and #6800 are #20 and #16 respectively - this could be interpreted as a JR NZ, $+24 instruction. To find out where this branch would go on a Non-Zero condition simply press 'O' when the Memory Pointer is addressing the displacement byte #16. The display will then update to centre around #6817, the required destination of the branch. Remember that relative displacements of greater then #7F (127) are treated as negative by the Z80 processor; 'O' takes this into account. See also the 'U' command in connection with 'O'. 'P' fill memory between specified limits with a specified byte. 'P' prompts for 'First:', 'Last:' and 'With:'. Enter hexadecimal numbers in response to these prompts; respectively, the start and end addresses (inclusive) of the block that you wish to fill and the byte with which you want to fill the block of memory. Example: P First: 7000 ENTER Last: 77FF ENTER With: 55 ENTER will fill locations #7000 to #7FF (inclusive) with the byte #55 ('U'). If the start address is greater than the end address then 'J' will be aborted. - Page 52 --------------------------------------------------------------------- 'Q' flip register sets. On entry to the 'front panel' display the set of registers displayed is the standard register set (AF, HL, DE, BC). The use of 'Q' will display the alternate register set (AF', HL', DE', BC') which is distinguished from the standard set by the single quote "'" after the register name. If 'Q' is used when the alternate register set is displayed then the standard set will be shown. 'SYMBOL SHIFT T' set a breakpoint after the current instruction and continue execution. Example: 9000 B7 OR A 9001 C20098 CALL NZ,#9800 9004 010000 LD BC,0 9008 21FFFF LD HL,-1 You are single-stepping the above code and have reached #9001 with a non-zero value in register A, thus the zero flag will be in a NZ state after the OR A instruction. If you now use '^Z' to continue single-stepping then execution will continue at address #9800, the address of the subroutine. If you do not wish to single-step through this routine then issue the ^T command when at address #9001 and the CALL will be obeyed automatically and execution stopped at address #9004 for you to continue single-stepping. Remember, ^T sets a breakpoint after the current instruction and then issues a ^K command. See the '^Z' command for an extended example of single-stepping. 'T' dis-assemble a block of code, optionally to the printer. You are first prompted to enter the 'First:' and 'Last:' addresses of the code that you wish to dis-assemble - enter these in hexadecimal as detailed in Section 1. If the start address is greater than the end address then the command is aborted. After entering these addresses you will be prompted with 'Printer?'; answer 'Y' (capital 'Y' only) to direct the dis-assembly to your printer stream or any other value to send output to the screen. - Page 53 --------------------------------------------------------------------- Now you are prompted with 'Text:' to enter, in hexadecimal, the start address of any textfile that you wish the dis-assembler to produce. If you do not want a textfile to be generated then simply press ENTER after this prompt. If you specify an address then a textfile of the dis-assembly will be produced, starting at that address, in a form suitable for use by GENS3. If you want to use a textfile with GENS3 then you must either generate it at, or move it to, the first address given by the assembler editor's 'X' command because this is the address of the start of the text expected by GENS3. You must also tell GENS3 where the end of the textfile is; do this by taking the 'End of text' address given by the dis-assembler (see below) and patching it into the TEXTEND location of GENS3 - see the GENS3 manual, Section 3.2. Then you must enter GENS3 by the warm start entry point, to preserve the text. If, at any stage when you are generating a textfile, the text would overwrite MONS3 then the dis-assembly is abortet - press any key to return to the Front Panel. If you specified a textfile address you are now asked to specify a 'Workspace:' address - this should be the start of a spare area of memory which is used as a primitive symbol table for any labels generated by the dis-assembler. The amount of memory needed is 2 bytes for each label generated. If you default by simply hitting ENTER then an address of #6000 (hex) is assumed. After this, you are asked repeatedly for the 'First:' and 'Last:' (inclusive) addresses of any data areas that exist within the block that you wish to dis-assemble. Data areas are areas of, say, text that you do not wish to be interpreted as Z80 instructions - instead these data areas cause DEFB assembler directives to be generated by the dis-assembler. If the value of the ASCII interpretation of the byte is given e.g. #41 is changed to 'A' after a DEFB. When you have finished specifying data areas, or if you do not wish to specify any, simply type ENTER in response to both prompts. The 'T' command uses an area at the end of MONS3 to store the data area addresses and so you may set as many data areas as there is memory available; each data area requires 4 bytes of storage. Note that using 'T' destroys any breakpoints that were previously set - see the 'W' command. The screen will now be cleared. If you asked for a textfile to be created then there will be a short delay (depending on how large a section of memory you wish to be dis-assembled) while the symbol table is constructed. This having been done, the dis-assembly listing will appear on the screen or printer - you may pause the listing at the end of a line by hitting ENTER or SPACE, subsequently hit CAPS SHIFT 5 to return to the 'front panel' display or any other key (except CAPS SHIFT 1) to ontinue the dis-assembly. If an invalid opcode is encountered then it is disassembled as NOP and flagged with an asterisk '*' after the opcode in the listing. - Page 54 --------------------------------------------------------------------- At the end of the dis-assembly the display will pause and, if you have asked for a textfile to be produced, the message 'End of text xxxxx' will be displayed; xxxxx is the address (in hexadecimal or decimal) that should be POKEd (low order byte first) into the GENS3 location TEXTEND in order that the assembler can pick up this dis-assembled textfile on a warm start. When the dis-assembly has finished, press any key to return to the 'front panel' display, apart from CAPS SHIFT 1 which will return you to BASIC. Labels are generated, where relevant (e.g. in C30078), in the form LXXXX where 'XXXX' is the absolute hex address of the label, but only if the address concerned is within the limits of the dis-assembly. If the address lies outside this range then a label is not generated, simply the hexadecimal or decimal address is given. For example, if we were dis-assembling between #7000 and #8000, then the instruction C30078 would be dis-assembled as JP L7800; on the other hand, if we were dis-assembling between #9000 and #9800 then the C30078 instruction would be disassembled as JP #7800 or JP 30720 if a decimal display is being used. If a particular address has been referenced in an instruction within the dis-assembly then its label will appear in the label field (before the mnemonic) of the dis-assembly of the instruction at that address but only if the listing is directed to a textfile. Example: T First:8B ENTER Last:9E ENTER Printer?Y Text: ENTER First:95 ENTER Last:9E ENTER First: ENTER Last: ENTER 008B FE16 CP #16 008D 3801 JR C,L0090 008F 23 INC HL 0090 37 SCF 0091 225D5C LD (#5C5D),HL 0094 C9 RET 0095 BF524E DEFB #BF,"R","N" 0098 C4494E DEFB #C4,"I","N" 009B 4B4559 DEFB "K","E","Y" 009e A4 DEFB #A4 - Page 55 --------------------------------------------------------------------- 'U' used in conjunction with the 'O' command. Remember that 'O' updates the memory display according to a relative displacement i.e. it shows the effect of a JR or DJNZ instruction. 'U' is used to update the memory display back to where the last 'O' was issued. Example: 7200 47 71F3 77 7201 20 71F4 C9 >7202 F2< >71F5 F5< 7203 06 71F6 C5 display 1 display 2 You are on display 1 and wish to know where the relative jump 20 F2 branches. So you press 'O' and the memory display updates to display 2. Now you investigate the code following #71F5 for a while and then wish to return to the code following the original relative jump in order to see what happens if the zero flag is set. So press 'U' and the memory display will return to display 1. Note that you can only use 'U' to return to the last occurence of the 'O' command, all previous uses of 'O' are lost. 'V' used in conjunction with the 'X' command. 'V' is similar to the 'U' command in effect except that it updates the memory display to where it was before the last 'X' command was issued. Example: 8702 AF 842D 18 8703 CD 842E A2 >8704 2F< >842F E5< 8705 44 8430 21 display 1 display 2 You are on display 1 and wish to look at the subroutine at #842F. So you press 'X' with the display centred as shown; the memory display then updates to display 2. You look at this routine for a while and then wish to return to the code after the original call to the subroutine. So press 'V' and display 1 will reappear. As with 'U' you can use this command only to reach the address at which the last 'X' command was issued, all previous addresses at which 'X' was used are lost. - Page 56 --------------------------------------------------------------------- 'W' sets a breakpoint at the Memory Pointer. A 'breakpoint', as far as MONS3 is concerned, is simply a CALL instruction into a routine within MONS3 that displays the 'front panel' thus enabling the programmer to halt the execution of a program and inspect the Z80 registers, flags and any relevant memory locations. Thus, if you wish to halt the execution of a program at #9876, say, then use the 'M' command to set the Memory Pointer to #9876 and then use 'W' to set a breakpoint at that address. The 3 bytes of code that were originally at #9876 are saved and then replaced with a call instruction that halts the execution when obeyed. When this CALL instruction is reached it causes the original 3 bytes to be replaced at #9876 and the 'front panel' to be displayed with all the registers and flags in the state they were just before the breakpoint was executed. You can now use any of the facilities of MONS3 in the usual way. Notes: When the breakpoint is encountered, MONS3 will emit a short tone through the Spectrum's speaker and wait for you to hit a key before returning to the Front Panel. MONS3 uses the area, at the end of itself, that originally contained the relocation addresses in order to store breakpoint information. This means that you may set as many breakpoints as there is memory available; each breakpoint requires 5 bytes of storage. When a breakpoint is executed MONS3 will automatically restore that memory contents that existed prior to the setting of that breakpoint. Note that, since the 'T' command also uses this area, all breakpoints are lost when the 'T' command is used. Breakpoints can onl be set in RAM. Since a breakpoint consists of a 3 byte CALL instruction a certain amount of care must be exercised in certain exceptional cases e.g. consider the code: 8000 3E 8008 00 8001 01 8009 00 8002 18 800A 06 8003 06 800B 02 >8004 AF< >800C 18< 8005 0E 800D F7 8006 FF 800E 06 8007 01 800F 44 If you set a breakpoint at #8004 and then begin execution of the code from location #8000 then register A will be loaded with the value 1, execution transferred to #800A, register B loaded with the value 2 and execution transferred to location #8005. But #8005 has been overwritten with the low byte of the breakpoint call and thus we now have corrupted code and unpredictable results will occur. This type of situation is rather unusual but you must attempt to guard against it - in this case single- - Page 57 --------------------------------------------------------------------- stepping the code would provide the answer; see the '^Z' command below for a detailed example of single-stepping. 'X' used to update the Memory Pointer with the destination of an absolute CALL or JP instruction. 'X' takes the 16 bit address specified by the byte at the Memory Pointer and the byte at the Memory Pointer +1 and then updates the memory display so that it is centred around that address. Remember that the low order half of the address is specified by the first byte and the high order half of the address is given by the second byte - Intel format. Example: say you wish to look at the routine that the code CD0563 calls; set the Memory Pointer (using 'M') so that it addresses the 05 within the CALL instruction and then press 'X'. The memory display will be updated so that it is centred around location #6305. See also the 'V' command in connection with 'X'. 'Y' enter ASCII from the Memory Pointer. 'Y' gives you a new line on which you can enter ASCII characters directly from the keyboard. These characters are echoed and their hexadecimal equivalents are entered into memory starting from the current value of the Memory Pointer. The string of characters should be terminated by CAPS SHIFT 5 and DELETE (CAPS SHIFT 0) may be used to delete characters from the string. When you have finished entering the ASCII characters (and typed CAPS SHIFT 5) then the display is updated so that the Memory Pointer is positioned just after the end of the string as it was entered into memory. 'SYMBOL SHIFT Z' single-step Prior to the use of '^Z' (or '^T') both the Program Counter (PC) must be set to the address of the instruction that you wish to execute. '^Z' simply executes the current instruction and then updates the 'front panel' to reflect the chanes caused by the executed instruction. - Page 58 --------------------------------------------------------------------- Note that you can single-step anywhere in the memory map (RAM or ROM) but that you should ensure that interrupts are not enabled at any time. You cannot single-step the Interface 1 ROM. There now follows an extended example which should clarify the use of many of the debugging commands available within MONS3 - you are urged to study it carefully and try it out for yourself. Let us assume that we have 3 sections of code shown on the next page in the machine, the first section is the main program which loads HL and DE with numbers and then calls a routine to multiply them together (the second section) with the result in HL and finally calls a routine twice to output the rsult of the multiplication to the screen (third section). The example begins on the next page..... - Page 59 --------------------------------------------------------------------- 7080 2A0072 LD HL,(#7200) ; SECTION 1 7083 ED5B0272 LD DE,(#7202) 7087 CD0071 CALL Mult 708A 7C LD A,H 708B CD1D71 CALL Aout 708E 7D LD A,L 708F CD1D71 CALL Aout 7092 210000 LD HL,0 . . . 7100 AF Mult OR A ; SECTION 2 7101 ED52 SBC HL,DE 7103 19 ADD HL,DE 7104 3001 JR NC,Mu1 7106 EB EX DE,HL 7107 B2 Mu1 OR D 7108 37 SCF 7109 C0 RET NZ 710A B3 OR E 710B 5A LD E,D 710C 2007 JR NZ,MU4 710E EB EX DE,HL 710F C9 RET 7110 EB Mu2 EX DE,HL 7111 19 ADD HL,DE 7112 EB EX DE,HL 7113 29 Mu3 ADD HL,HL 7114 D8 RET C 7115 1F Mu4 RRA 7116 30FB JR NC,Mu3 7118 B7 OR A 7119 20F5 JR NZ,Mu2 711B 19 ADD HL,DE 711C C9 RET 711D F5 Aout PUSH AF 711E 0F RRCA 711F 0F RRCA 7120 0F RRCA 7121 0F RECA 7122 CD2671 CALL Nibble 7125 F1 POP AF 7126 E60F Nibble AND %1111 7128 C690 ADD A,#90 712A 27 DAA 712B CE40 ADC A,#40 712D 27 DAA 712E FD213A5C LD IY,#5C3A 7132 D7 RST #10 7133 C9 RET . . 7200 1B2A DEFW 10779 7202 0300 DEFW 3 - Page 60 --------------------------------------------------------------------- Now we wish to investigate the above code either to see if it works or maybe how it works. We can do this with the following set of commands - it should be noted that this is merely one way of stepping through the code, it is not necessarily efficient but should serve to demonstrate single stepping: M:7080 ENTER set Memory Pointer to #7080 7080. set Program Couner to #7080 ^Z single step. ^Z single step. ^Z follow the CALL. M:7115 ENTER skip te pre-processing of the numbers. W set a breakpoint. ^K continue execution from #7100 up to breakpoint. ^Z single step. ^Z follow the relative jump. ^Z single step. ^Z " ^Z " ^Z " ^Z " ^Z " ^Z " ^Z return from multiply routine. ^Z single step. ^Z follow the CALL. M:7128 ENTER set Memory Pointer to interesting bit. ^K continue execution from #711D to breakpoint. ^Z single step. ^Z " ^Z " ^Z " , have a look at the return address. W set breakpoint there ^K and continue. ^Z single step. , return from Aout routine W ^K ^Z single step. ^T obey the whole CALL to Aout. Please do work through the above example, first typing in the code of the routines (see 'Modifying Memory' below), or using GENS3, and then obeying the commands detailed above. You will find the example invaluable as an aid to understanding how to trace a path through a program. - Page 61 --------------------------------------------------------------------- '"' SYMBOL SHIFT P this command is exacltly the same as the 'L'ist command except that the output goes to the printer stream instead of to the screen. Remember that, at the end of a page, you press CAPS SHIFT 5 to return to the 'front panel' or any other key (except CAPS SHIFT 1) to get another page. Modifying Memory. The contents of the address given by the Memory Pointer may be modified by entering a hexadecimal number followed by a terminator (see Section 1). The two least significant hex digits (if only one digit is entered then it is padded to the left with a zero) are entered into the location currently addressed by the Memory Pointer and then the command (if any) specified by the terminator is obeyed. If the terminator is not a valid command then it is ignored. Examples: F2 ENTER #F2 is entered and the Memory Pointer advanced by 1. 123 CAP SHIFT 8 #23 is entered and the Memory Pointer advanced by 8. EM:E00_ #0E is entered at the current Memory Pointer and then the Memory Pointer is updated to #E00. Notice that a space ('_') has been used to terminate the 'M' command here. 8CO #8C is entered and the Memory Pointer is updated (because of the use of the 'O' command) to the destination of the relative offset #8C i.e. to its current value - 115. 2A5D_ #5D is entered and the Memory Pointer is not changed since the terminator is a space, not a command. Modifying Registers. If a hexadecimal number is entered in response to the '>' prompt and is terminated by a period, '.', then the number specified will be entered into the Z80 register curently addressed by the right arrow '>'. On entry to MONS3 '>' points to the program Counter (PC) and so using '.' as a terminator to a hex number initially will modify the program counter. Should you wish to modify any other register then use '.' by itself (not as a terminator) and the pointer '>' will cycle round the registers PC to AF. Note that is is not possible o adress (and thus change) either the Stack Pointer (SP) or the IR registers. - Page 62 --------------------------------------------------------------------- Examples: Assume that the register pointer '>' is initially addressing the PC. . point to IY. . point to IX. 0. set IX to zero. . point to HL. 123 set HL to #123. . point to DE. . point to BC. E2A7 set BC to E2A7. . point to AF. FF00. set A to #FF and reset all the flags. . point to PC. 8000. set the PC to #8000 Note that '.' can also be used to modify the alternate register set if this is displayed. Use to 'Q' command to flip the display of the register sets. - Page 63 --------------------------------------------------------------------- APPENDIX AN EXAMPLE FRONT PANEL DISPLAY 710C 2007 JR NZ,#7115 >PC 710C 20 07 EB C9 EB 19 EB SP D0AF 8A 70 06 03 0A 03 0D IY CF6A 0D 11 0C 0F 09 18 18 IX D09F 04 03 04 00 00 00 1B HL 2A1B DF FE 29 28 02 CF 02 DE 0000 F3 AF 11 FF FF C3 CB BC 0004 FF C3 CB 11 2A 5D 5C AF 0304 V IR 3F7C 7100 AF 7108 37 7110 EB 7101 ED 7109 C0 7111 19 7102 52 710A B3 7112 EB 7103 19 710B 5A 7113 29 7104 30 >710C 20< 7114 D8 7105 01 710D 07 7115 1F 7106 EB 710E EB 7116 30 7107 B2 710F C9 7117 FB > Shown above is a fairly typical 'front panel' display - the display is one actually obtained while single-stepping the Mult routine given in the example of the 'Z' command. The first 9 lines of the display contain the Z80 registers; the name of the register first (PC to IR), then (for PC to BC) the value presently held in the register and finally the contents of the 7 memory locations starting from the address held in the register. The Flag register is decoded to show the flags currently set in the bit order that they are used within the register - if the Flag register was set to #FF then the display following AF would look like 00FF SZ H VNC i.e. the sign, zero, half-carry, parity/overflow, add/subtract and carry flags are all set. A register pointer '>' points to the register currently addressed; see Section 2 - Modifying Registers. The 24 byte memory display below the register display is organised as the address (2 bytes, 4 characters) followd by the contents (1 byte, 2 characters) of the memory at that address. The display is centred around the current Memory Pointer value, indicated by '> <'. Commands (see Section 2) are entered on the bottom line of the screen in response to the prompt '>'. The display is updated after each command is processed. - Page 64 --------------------------------------------------------------------- -notes-