THE COMPLETE MACHINE CODE TUTOR by MALCOLM EVANS 48K SPECTRUM Copyright 1984 New Generation Software Ltd. Bath, Avon LOADING INSTRUCTIONS This program is arranged on four sides of tape. To load the program type LOAD "" using side 1. This will load in the screen and program/simulator. When instructed stop the tape. Do not press BREAK during the loading of the simulator. You will then be asked whether you wish to load lessons. If no (N) you will enter straight into the editor part of the simulator. This is not recommended for beginners. You may escape by pressing BREAK. If yes (Y) you will be requested to load the required group of lessons. Choose the desired section and start the tape recorder. The group you have chosen, will appear on the screen. If you have selected the wrong group, pressing BREAK will stop the load, and enable you to load another section The program and lessons are arranged on the cassette tapes as follows. SIDE 1 - Program/simulator : Lessons 1 - 9 SIDE 2 - Lessons 10 - 17 : Lessons 18 - 25 SIDE 3 - Program/simulator : Lessons 18 - 25 SIDE 4 - Lessons 26 - 35 : Lessons 1 - 9 ASSEMBLER INSTRUCTIONS The assembler accepts all Z80 instructions as included in the lesson summaries. In addition it will accept the following instructions itself: DEFB n : Define byte. This allocates the Next memory location for storage. (This may be labelled), and initially loads it with n. The simulator will continually display the contents of the location in decimal or hex. DEFW nn : Define word. This allocates the next two memory locations for storage (may be labelled), and initially loads it with the two byte number nn. The simulator will continually display the contents of these locations as a single decimal or hex number. BIN n : This is the same as DEFB, except that The simulator displays the memory contents in binary form. N is a decimal or hex number. The assembler will also accept labels. A label is defined in relationship to numbers as follows: Decimal number : Any string containing only 0-9 Hexadecimal number : Any string containing only 0-9 or A-F. It may be distinguished from decimal by following it with a H. Label : Labels a memory location. Any string not covered by decimal or hexidecimal numbers above, register names or conditional letters i.e. C, NC, Z, NZ, etc. The maximum length is 6 characters. ERROR MESSAGES - ASSEMBLER Instruction unknown - First part of mnemonic not recognised. Space missing - Space missing after first part of mnemonic i.e. LDA,5. Missing space or , - Space or , missing after second pair of mnemonic i.e. LD A5 or SUB AM Error after instr. - Error after first part of mnemonic which the assembler was unable to recognize as any other defined error. Number missing - Part of mnemonic missing. Could be a number. Bracket missing - A bracket missing. Number too large - 16 bit number greater than 65535. Label too long - Labels can only have up to 8 characters. Label not found - Label appears in instruction but not declared in label column. No DEFM or DEFW - Label with no instruction. Can only add IX/IY - SBC IX/IY or ADC IX/IY found. Offset too big - Offset in (IX+d) or (IY+d) instruction greater than 255. Offset missing - No offset in (IX+d) or (IY+d) instruction. ERROR MESSAGE - SIMULATOR - Your program has caused the PC to jump to an adress which is not the beginning of one of your instruction lines. You are trying to run code in allocated storage area - Your program has caused the PC to jump to an adress which has been allocated as storage. You are about to affect memory area not allocated to you - you are about to load a memory location not allocated to you. Your allocated area is 16384 (4000h) to 23295 (5AFFh) and 32000 (7D00h) to 32192 (7DC0h) You are about to write to memory which will affect your program - you are about to load a memory location within your program instructions. The stack pointer is outside allocated memory area - The stack pointer has moved outside the area 32193 (7DC1h) to 32255 (7DFFh). There are too many registers called up - your program uses more registers than the simulator can display. The program can be run, but only those registers displayed can be shown. The lessons in this program are arranged in four groups. Upon loading of each section an introduction appears on the screen. The menu for the group of lessons can then be obtained by pressing SPACE, at any time whilst in a lesson or example. Pressing BREAK (CAPS SHIFT + SPACE) will return you to the menu. The following is a complete list of all keys used at various stages with a full description of their function. MENU ENTER : Will enter any lesson or example highlighted on the menu. SPACE : Pressing this key allows you to choose which item to enter. LESSON AND EXAMPLE TEXT SPACE : Pressing thls key will display the next page. At the end of each lesson it will effect a return to menu BREAK : Will return you to the menu at any time. SIMULATOR - All keys auto-run. RUN : This clears all registers and starts program running. ANY KEY : If in running state will perform the highlighted instruction. STOP : This stops the running of the program. (a+symbol shift) EDIT : Pressing this key enters the editor, (I+ symbol allowing you to modify or re-write the shift) program. G : This swops the display between decimal and hexadecimal notation. This key is operative only when the program is NOT running. BREAK : Will return you to the menu. Once completed if you wish to repeat the exercise then press RUN. EDITOR - All keys auto-run CURSOR KEYS : Pressing these will allow you to (5,6,7,8 + move the cursor in the direction of CAPS SHIFT) the arrows. & : This clears the editor screen and (6 + symbol memory and returns the cursor to shift) the start of the screen. SPACE : Tabs to beginning of instruction when in label column, elsewhere a space will be created. ENTER : This moves the cursor to the start of the next line. DELETE : This deletes the character to the (0+CAPS left of the cursor and shifts the SHIFT) cursor one space to the left. STOP : Initiates assembly of the program on screen. If assembled correctly the simulator mode is entered. If an error is found then an error statement is displayed against the appropriate line of the program and the editor waits for correction. BREAK : Will return you to the menu. The editor allways displays letters in capitals. However CAPS SHIFT is not required. INTRODUCTION TO LESSONS The Complete Machine Code Tutor contains 35 lessons covering all the instructions on the z80 processor. Which is the processor in your Spectrum computer. All the lessons are dealt with in great detail on screen. And in many cases are followed by example programs, which you can use as exercises by modifying them yourself. There is no danger that you might crash the system. There now follows a list of all the lesson headings, together with an indication of those lessons that are followed by examples. Under each heading there is a summary of instructions which will become clear to you as you progress through the tutor. These summaries are intended as a permanent record of instructions, to which you can easily refer for revision purposes, without having to refer back to the screen text. LESSON 1 - Registers and Memory Initially we only consider A,B,C,D, E,H And L registers. LESSON 2 - Simple Load Instructions The following instructions are covered: LD r,r' Where r and r' are any of the following: A,B,C,D,E,H and L. LD r,n Where n is a number 0 - 255. LD A,(nn) Where nn is a memory location 0 - 65535. LD (nn),A Where nn is a memory location 0 - 65535. Examples follow this lesson. LESSON 3 - Register Pairs A number in a register pair is 256 x the high byte + the low byte. The following instructions are covered: LD dd,nn Where dd is any register pair BC, DE and HL. nn is a number 0 - 65535. LD dd,(nn) where nn is address of a memory location 0 - 65535. LD (nn),dd where nn is address of a memory location 0 - 65535. EX DE,HL Exchanges register contents. Examples follow this lesson LESSON 4 - Indirect Adressing The following instructions are covered: LD r,(HL) Where r is any single register - LD (HL),r A,B,C,D,E,H OR L. LD A,(BC) LD A,(DE) LD (BC),A LD (DE),A Examples follow this lesson. LESSON 5 - Additions and the Carry Flag Additions with Accumulator and HL register pair are discussed as well as ADD with Carry. The following lnstructions are covered: ADD A,n Where n is a number 0 - 255. ADD A,R Where r is any single register. ADD A,(HL) ADD HL,BC ADD HL,DE ADC A,n ADD with Carry. ADC A,r ADC A(HL) ADC HL,BC ADC HL,DE 2 examples follow this lesson. LESSON 6 - Subtraction and the carry flag Subtraction with and without carry on the accumulator and HL register pair are discussed. The following instructions are covered: SUB n ) SUB r ) Subtract from A, n, r or (HL) SUB (HL) ) SBC A,n ) SBC A,r ) Subtract from A with carry SBC A,(HL) ) SBC HL,BC ) Subtract from HL with carry SBC HL,DE ) SCF Set carry flag CCF Compliment carry flag 2 examples follow this lesson. LESSON 7 - Increment And Decrement Instructions The following instructions are covered: INC n INC (HL) INC dd DEC r DEC (HL) DEC dd Examples follow this lesson LESSON 8 - The zero flag No new instructions are covered in this lesson, which is included to show you the effect on the zero flag of all the instructions considered in previous lessons. A table of the effects of all instructions on all flags is given in appendix (A) examples follow thls lesson LESSON 9 - Compare If n is the number with which A is compared, then the following results: Carry Zero A greater than n 0 0 A equals n 0 1 A less than n 1 0 The following instructions are covered: CP n Compares A with n (o-255) CP r Compares A with register r CP (HL) Compares A with memory location (HL) Examples follow this lesson LESSON 10 - Conditional & Unconditional Jumps The following instructions are covered: JP nn JP (HL) JR NC,nn Jump if carry flag not set JP C,nn Jump if carry flag set JP NZ,nn Jump if zero flag not set JP Z,nn Jump if zero flag set Examples follow this lesson LESSON 11 - Relative Jumps The following instructions are covered: JR e Where e is the displacement in the range 127 to -128. JR NC,e JR C,e JR NZ,e JR Z,e DJNZ e Decrement and jump on non zero 2 examples follow this lesson. LESSON 12 - The Stack The stack and the stack pointer are introduced. The following instructions are covered: PUSH dd Where dd is AF, BC, DE or HL. From now on dd can be considered as BC, DE, HL or SP. POP dd LD SP,nn LD SP,(nn) LD (nn),SP LD SP,HL ADD HL,SP ADC HL,SP SBC HL,SP INC SP DEC SP EX (SP),HL Examples follow this lesson. LESSON 13 - Calls To Subroutines The following instructions are covered: CALL RET Unconditional CALL NC,nn RET NC No carry CALL C,nn RET C Carry set CALL NZ,nn RET NZ Not zero CALL Z,nn RET Z Zero set 2 examples follow this lesson. LESSON 14 - Binary Notation This lesson is about a whole new number base - binary. This is a system of using only two different numbers, one and zero. In each digit column, a flag is an excellent example of a binary digit. This is because it can only hold a value of one or zero. After reading the lesson about binary, you may find this reference chart useful: Values of Bit 7 TO Bit 0: Bit number : 7 6 5 4 3 2 1 0 Values : 128 64 32 16 8 4 2 1 Examples follow this lesson LESSON 15 - Hexadecimal Notation Hexadecimal notation is discussed at great length in this lesson, but the following table will prove an invaluable reference:- Decimal Binary Hexadecimal 0 0000 0 1 0001 1 2 0010 2 3 0011 3 4 0100 4 5 0101 5 6 0110 6 7 0111 7 8 1000 8 9 1001 9 10 1010 A 11 1011 B 12 1100 C 13 1101 D 14 1110 E 15 1111 F Examples follow this lesson. LESSON 16 - Binary Coded Decimal Notation The instruction DAA (decimal adjust accumulator) is introduced. Examples follow this lesson. LESSON 17 - Positive & Negative Number Notation The instructions introduced are CPL (complement) and NEG (negate). As well as the overflow and sign flags. A table of the effects of all instructions on the overflow and sign flags is given in appendix (A). Examples follow this lesson. LESSON 18 - Parity The parity flag and its uses are introduced. A table of the effects of all instructions on the parity flag is given in appendix (A). LESSON 19 - The flag register and AF register pair LESSON 20 - Sign & P/V flags in instructions the following instructions are covered: JP PO,nn CALL P0,nn RET PO Parity odd = 0 JP PE,nn CALL PE,nn RET PE Parity even = 1 JP P,nn CALL P,nn RET P Sign +ve JP M,nn CALL M,nn RET M Sign -ve If the condition is not met, the program will not jump, call a subroutine or return. Examples follow this lesson. LESSON 21 - Bit Manipulation The following instructions are covered: SET n,r Where n is the bit number 0-7. SET n,(HL) RES n,r RES n,(HL) BIT n,r BIT n,(HL) Examples follow this lesson LESSON 22 - Logical Instructions The following instructions are covered: AND n AND r AND (HL) OR n OR r OR (HL) XOR n XOR r XOR (HL) Examples follow this lesson LESSON 23 - Shift Instructions Shift instructions are pictorially illustrated in appendix (B). The following Instructions are covered: SRA r Divides +ve and -ve numbers by 2. SRA (HL) SRL r Divides +ve numbers 0 - 255 by 2. SRL (HL) SLA r Multiplies +ve and -ve numbers by 2. SLA (HL) Examples follow this lesson. LESSON 24 - Rotate Instructions Rotate instructions are pictorially illustrated in appendix (B). The following instructions are covered: RLC r Rotate r left carry duplicates RLC (HL) RLCA Rotate A left carry duplicates RL r Rotate r and carry left RL (HL) RLA Rotate A and carry left RRC r Rotate r right, carry duplicates RRC (HL) RRCA Rotate A right, carry duplicates RR r Rotate r and carry right RR (HL) RRA Rotate A and carry right Examples follow this lesson LESSON 25 - Decimal Rotate Decimal rotate instructions are pictorially illustrated in appendix (B). The following lnstructlons are covered: RLD Rotate left decimal (x10) RRD Rotate right decimal(/10) Examples follow this lesson. LESSON 26 - Index Registers. The IX or IY registers can replace the HL register in all instructions except ADC HL,dd SBC HL,dd and EX DE,HL The following instructions are covered: LD r,(IX+d) LD IX,nn LD SP,IX LD (IX+d),r LD IX,(nn) LD (IX+d),n LD (nn),IX EX (SP),IX ADD A,(IX+d) INC (IX,d) AND (IX+d) ADC A,(IX+d) DEC (IX,d) OR (IX+d) SUB (IX+d) XOR (IX+d) SBC A,(IX+d) CP (IX+d) ADD IX,dd INC IX DEC IX SLA (IX+d) SRA (IX+d) SRL (IX+d) RLC (IX+d) RL (IX+d) RRC (IX+d) RR (IX+d) SET n,(IX+d) RES n,(IX+d) BIT n,(IX+d) JP (IX) Examples follow this lesson. LESSON 27 - The Alternative Set Of Registers The following instructions are covered: EX AF,AF' Exchanges the contents of AF and AF' EXX Exchanges BC,DE and HL, with BC',DE' and HL' respectively. Examples follow this lesson LESSON 28 - Input And Output Instructions The following lnstructions are covered: IN A,(N) Where n is the number of the input IN r,(C) port (0-255) IN F,(n) OUT (n),A OUT (C),r Examples follow this lesson LESSON 29 - Block Instructions LESSON 30 - Block Transfer Instructions The following instructions are covered: LDI Pointer incremented LDIR Pointer incremented and repeated until number found or BC=0 LDD Pointer decremented LDDR Pointer decremented and repeated until number found or BC=0 Examples follow this lesson LESSON 31 - Block Search The following instructions are covered: CPI Pointer incremented CPIR Pointer incremented and repeated until number found or BC=0 CPD Pointer decremented CPDR Pointer decremented and repeated until number found or BC=0 Examples follow this lesson LESSON 32 - Block Input/Output Instructions The block input instructions covered are: INI Incrementing INIR Incrementing and repeating IND Decrementing INDR Decrementing and repeating The block output instructions covered are: OUTI Incrementing OTIR Incrementing and repeating OUTD Decrementing OTDR Decrementing and repeating Examples follow this lesson LESSON 33 - Processor Control Instructions The following instructions are covered: NOP HALT RST n Where n = 00H 08H 10H 18H 20H 28H 30H or 38H LD A,R LD R,A LD A,I LD I,A Examples of the use of the refresh register follow this lesson. LESSON 34 - Interrupts The following instructions are covered: EI Enable interrupts DI Disable interrupts IM0 ) IM1 ) Interrupt modes IM2 ) RETI Return from interrupt RETN Return from non-maskable interrupt LESSON 35 - Finale GLOSSARY Assembly language - A language using mnemonics to represent machine code operations. A low-level language. An assembly language program can not itself be run until it is assembled. BINARY - Two. In binary arithmetic the digits 0 and 1 are used to represent numbers. BINARY CODED DECIMAL (BCD) - A system where a nibble represents one decimal number, therefore a byte can represent two decimal numbers. BIT - One single binary digit. Either a one or a zero. BUG - An error or undesirable aspect in a program, which prevents a program from working correctly or not at all. BYTE - A group of binary bits. Usually 8, considered as one unit. CHARACTER - An element of a set of symbols, such as a letter or number, or special symbol. CHIP - Common name for integrated circuit. Derived from the small piece of silicon on which the integrated circuit is chemically formed. COMPUTER - A machine that accepts data, acts upon it, and supplies the results of the processing as a result of certain instructions. A collective noun describing the processor and I/O devices. CRASH - Term used to describe the computer 'locking up' and not accepting any input from the keyboard. The only solution is to turn the computer off and then on again. CURSOR - A flashing thin line used to indicate where data is expected to be entered on a VDU. DATA - A piece of information which the computer can process. EDITING - The process of changing data before it is committed to the processor. EXECUTE - To carry out the instructions in a program. A microprocessor executes a program by reading and acting on the instructions. GRAPHICS - Term describing the display of data in pictorial form. Pictures on screen are displayed using pixels. HARDWARE - Parts of the computer that physically exist, the computer and a printer for example. HEXADECIMAL - A number base using 16 different digits for each number column. The digits 0-9 and A-F are commonly used. INSTRUCTlON - A certain action to be taken by the processor. A machine code program is made up of instructions. MACHINE CODE - Binary representation of the instructions of the microprocessor. Machine code can be acted upon by the microprocessor without any further translation. MEMORY - Collection of integrated circuits in which data is stored. Each binary bit is stored as an electrical signal within the IC. Memory is classified as ROM or ram and its size is measured K (kilobytes). MICROPROCESSOR - An integrated circuit that contains all the components to perform the basic data processlng operations, all in one package. A microprocessor must be connected to memory and I/0 devices before it can be used. MNEMONIC - A group of 3-4 characters representing a machine code instruction. Each mnemonic is translated by an assembler into a machine code instruction. NIBBLE - A group of four bits. There are two nibbles per byte. OBJECT PROGRAM - A program in machine code. The source program, which cannot be executed by the processor, is assembled by the assembler which generates an object program. This object program resides in memory, and can be executed by the processor. OPERATING SYSTEM - A machine code program, part of the systems software, which enables the processor to perform the data processing and control functions. PAGE - When used in conjunction with memory, means 256 bytes of memory. PROGRAM - A collection of instructions to make the microprocessor perform a certain task. RAM - Random access memory. This kind of memory may be written to or read from. This kind of memory is used to store the program that is being developed. If you turn the computer off, all data contained in RAM will be lost. ROM - Read only memory. This kind of memory is set up at the factory where the computer ls made. It usually houses the operating system and other programs necessary each time the computer is turned on. Turning the computer off and then back on again has no effect on ROM. SOFTWARE - A non-physical part of a computer such as a program. SOURCE PROGRAM - The program that consists of mnemonics that can be understood by humans. This program cannot be executed until it is assembled. APPENDIX A Effect Of Instructions On Flags Single Register Instructions Instruction Carry Zero P/V Sign ALL LD............... + + + + EXCEPT LD A,I & LD A,R + ! !(1) ! ADD, ADC, SUB, SBC, CP ! ! v ! INC, DEC + ! v ! DAA ! ! p ! NEG ! ! p ! Shift & Rotate specific. on A ! + + + RLD, RDD + ! p ! All other shift & rotates on r ! ! p ! AND, OR, XOR 0 ! p ! BIT + ! ? ? SET, RES + + + + CCF ! + + + SCF 1 + + + Effect Of Instructions On Flags Register Pair Operations Instruction Carry Zero P/V Sign All LD instructions + + + + All exchange instructions + + + + ADD ! + + + ADC, SBC ! ! v ! INC, DEC + + + + PUSH, POP + + + + NOTATION: + Not affected v P/V owerflow p P/V parity 0 Flag reset 1 Flag set ? Flag state unknown ! Affected according to instruction Effect Of Instructions On Flags Miscellaneous Instructions Instruction Carry Zero P/V Sign All JP, JR, CALLS, RET & DJNZ + + + + LDI, LDD + + !(2) + LDIR, LDDR + + 0 + CPI, CPIR, CPD, CPDR + !(3) !(2) ! IN A,(n) OUT(n),A + + + + OUT (C),r + + + + IN R,(C) + ! p ! INI, IND, OUTI, OUTD + !(4) ? ? INIR, INDR, OTIR, OTDR + 1 ? ? NOP, HALT, DI, EI, IM + + + + NOTES: (1) P/V displays state of interrupt enable flag (2) P/V = 0 if BC = 0 IF NOT P/V = 1 (3) Z = 1 IF A = (HL) IF NOT Z = 0 (4) Z = 1 IF B = 0 IF NOT Z = 0 APPENDIX B Shift & Rotate Instructions Pictorial Description 旼컴컴컴컴컴컴컴컴컴컴컴� 旼컴� � 旼컴컴컴컴컴컴컴컴커 � RLC, RLCA � C <컴좔� 7 0 <컴� 읕컴� 읕컴컴컴컴컴컴컴컴켸 旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� � 旼컴� 旼컴컴컴컴컴컴컴컴커 � RL, RLA 읕캑 C <컴컴� 7 0 <컴� 읕컴� 읕컴컴컴컴컴컴컴컴켸 旼컴컴컴컴컴컴컴컴컴컴컴� � 旼컴컴컴컴컴컴컴컴커 � 旼컴� RRC, RRCA 읕�> 7 0 쳐좔�> C � 읕컴컴컴컴컴컴컴컴켸 읕컴� 旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� � 旼컴컴컴컴컴컴컴컴커 旼컴� � RR, RRA 읕�> 7 0 쳐컴�> C 쳐켸 읕컴컴컴컴컴컴컴컴켸 읕컴� 旼컴� 旼컴컴컴컴컴컴컴컴커 SLA � C <컴컴� 7 0 <컴� 0 읕컴� 읕컴컴컴컴컴컴컴컴켸 旼컴컴컴컴컴컴컴컴커 旼컴� SRA 旼컴> 7 0 쳐컴�> C � � 읕쩡컴컴컴컴컴컴컴켸 읕컴� 읕컴컴� 旼컴컴컴컴컴컴컴컴커 旼컴� SRL 컴컴> 7 0 쳐컴�> C � 읕컴컴컴컴컴컴컴컴켸 읕컴� 旼컴컴컴컴컴컴컴컴컴컴� 旼컴컴컴컫컴컴좔컴� 旼컴컴컴컫컴�\/컴커 RLD A � 7 4 � 3 0 � � 7 4 � 3 0 � (HL) 읕컴컴컴컨컴컴^컴켸 읕컫컴^컴좔컴쩡컴켸 읕컴컴컴컴컴� 읕컴컴켸 旼컴컴컴컴컴� 旼컴컴커 旼컴컴컴컫컴컴좔컴� 旼�\/컨컴쩡컴\/컴커 RRD A � 7 4 � 3 0 � � 7 4 � 3 0 � (HL) 읕컴컴컴컨컴컴^컴켸 읕컴컴컴컨컴컫컴컴� 읕컴컴컴컴컴컴컴컴컴컴�