Z88 Developers' Notes
Previous Contents Next

23. Miscellaneous useful information
 

The expanded and non-expanded machine

When a Z88 has 128K or more of RAM in slot 1, it becomes expanded. The latest V4 of the operating system is expanded automatically if internal RAM has been upgraded to 128K or more. For previous versions of the Z88 operating system only the first rule is obeyed. The differences between the expanded and non-expanded computers are as follows: 

Property                Expanded                Non-expanded
Size of BBC BASIC       40K                     8K
Maximum map width       256 pixels              96 pixels
User characters         64                      16 (but see below)
Value of EOF#-1         -1                      0
Some users will want to use extra memory, for filing for example, without the burden of a 40K BASIC. If all your BASIC programs fit comfortably within the ordinary 8K it is unhelpful to have to carry the extra 32K around, thus using slot 2 or slot 3 to expand the memory does not expand the machine (V3 or earlier operating systems), but just increases memory size (note that using slot 3 for RAM causes a very heavy power drain on the Z88, due to the lack of special power saving hardware in this slot). The unexpanded machine can use 64 user characters, but if an 80 pixel map is used, the last 48 of these will be overwritten by map information when PipeDream is used (or another application that write to the high resolution map). Reducing the map width to 64 pixels, or not using the map at all, allows for free use of all 64 user characters. The file attributes for BASIC's -1 channel ($FFFF) all hold interesting information: 
PTR#-1      high word = no. of free handles in the system. low word = ROM
            version code (=3 for 2.2 and 3.0 versions).

EXT#-1      free memory. This is an approximation and should be interpreted
            with care. It is similar to the memory free indicators given by
            PipeDream and the Diary (Z80asm uses it too).

EOF#-1      -1 = machine is expanded. 0 = standard 32K machine
This information can be accessed by applications by using the OS_Frm system call, to read file attributes, and specifying a handle of $FFFF in the IX register pair. Note that although the sequential pointer (PTR) and extent (EXT) are returned as 4 byte values in DE and BC registers, the end of file (EOF) result is returned in Fz, with Fz = 1 indicating the end of file (ie. TRUE or 1) and Fz = 0 otherwise (ie. FALSE or 0).
 

Extra CLI features 

<SQUARE> + S            T-direct output to ":RAM.-/s.sgn".
<SQUARE> + K            T-direct input to ":RAM.-/k.sgn".
<SQUARE> + P            T-direct output to :PRT.0
<DIAMOND><LEFT-SHIFT>   Freeze screen output
If there is an EPROM, which contains a file called "boot.cli", present in slot 3 at the time of a reset (soft or hard) then it will be loaded into :RAM.- and executed as a CLI file.

Note: :RAM.- files are dangerous under the version 2.2 or 3.0 of the operating system - see below for details.
 
 

Memory for files and applications

Each RAM card is given an allocation of space by the system which is useable by the RAM filing device associated with that slot. This allocation is always less than total RAM available in that card. Applications (and the special device :RAM.-) can use the remaining memory as well as the memory allocated to files. Because of this approach, the values given for free memory are sometimes confusing. The free memory indicators return space available to applications, which will generally be rather less than that available to files.

The device :RAM.- can use memory from anywhere in the system, and as such is it very useful for large files. Due to a bug in versions 2.2 (3.0) in the operating system, if any files are stored in the device when a soft reset occurs, the system becomes badly confused, and it is very likely that a crash will follow sometime later. If you need to use :RAM.- files, then it is vital that they are deleted immediately after use. The features described in the previous section all use :RAM.- and if these operations are used, then the files generated should be deleted at the first opportunity.

NOTE: V4 has fixed the :RAM.- problem. Some foreign V3.xx versions contains the fix as well. You will probably be aware of this on your own Z88.
 

PipeDream format

The PipeDream file format is designed to facilitate manipulation by other programs. No control characters, or characters above ASCII value 127 are used in the file, unless they have been explicitly typed in (ISO characters), apart from Carriage Return (CR) characters which are used as separators. The files are sequential, and can be edited by any text editor.

PipeDream uses a special form of construct to add special information about the structure of the file. All constructs begin and end with an ASCII percent sign '%'. Immediately after the first percent sign come one or more alphabetic characters which identify the construct. Between these characters and the final percent sign, can come any information which is relevant to the construct.

At the start of the file is a group of constructs that identify what the values of Options Page Parameters are for the file. This is followed by the main body of the file.

Each column in the file is preceeded by a column construct which gives details about the column followed by all the slots in the column. Every slot that is defined in that column has an entry.

Each entry is separated from the next one with a CR character. On each line there can be a collection of constructs giving details about the slot.

For each column in the file there is a column construct, followed by all the entries for that column, until the end of file.

Options Page construct

%OP%parameter value CR 

parameter   two characters identifying the parameter
value       the value of the parameter
CR          Carriage Return ($0D)
The various parameter values are: 
AM          Auto/manual
BM          Bottom margin
BO          Borders
DE          Title
DP          Decimal places
FM          Footer margin
FO          Footer
HE          Header
HM          Header margin
IW          Insert on wrap
JU          Justify
LM          Left margin
LP          Leading characters
LS          Line spacing
MB          Minus/Brackets
PA          Pages
PL          Page length
PS          Page start no.
RC          Rows/Columns
TM          Top margin
TN          Text/Numbers
TP          Trailing characters
WR          Wrap
Column construct

%CO: column, width, wrap-width% 

column      letter identifying the column, eg. A
width       decimal number giving the column width
wrap-width  decimal number giving the wrap-width
These constructs can appear anywhere in the entry for each slot: 
%B%         bracket format
%C%         centre format
%Dn%        decimal places. n gives the number
%DF%        floating format
%F%         free align
%Hn%        highlight character: n gives the number (1 to 8)
%JL%        justify left
%JR%        justify right
%L%         left align
%LC%        leading character format
%LCR%       LCR align
%Pn%        page break: n gives the argument, 0 for unconditional
%PC%        per cent character
%R%         right align
%TC%        trailing character format
%V%         slot is a number slot
General format

construct text construct text ... CR 

construct   one of the constructs above
text        ASCII characters being the slot contents
CR          Carriage Return ($0D)
Diary format

Each day the diary uses (an active day) is headed by a date. This date is in the form:

%dd,mm,yyyy
The % character is represented as %%

The remainder of a diary file is simply straight text.
 

File EPROM format

The following is the format used in file EPROMs. Unfortunately this is not the conventions used by the DOR system. However, it is sufficient for traversing through the file contents. With this information you can program an application that can retreave previously 'deleted' (overwritten) files. The format is as follows: 

$0000       File entry
...         File entry
... 
...         Latest file entry
...         $FF's until
$3FC0       $00's until
$3FF7       $01
$3FF8       4 byte random id
$3FFC       size of card in banks (2=32K, 8=128K, 16=256K)
$3FFD       sub-type, $7E for 32K cards, and $7C for 128K (or larger) cards
$3FFE       'o'
$3FFF       'z' (file eprom identifier, lower case 'oz')
A file entry has the form: 
1 byte      n           length of filename
1 byte      x           '/' for latest version, $00 for old version (deleted)
n-1 bytes   'xxxx'      filename
4 bytes     m           length of file (least significant byte first)
m bytes                 body of file
When a file is saved to EPROM which has the same name as an exising file, the byte following the filename length, is set to zero, thus marking the file deleted. However, the name length and contents of the old file are all intact and so by directly reading the EPROM, old files can be recovered.

Previous Contents Next
Miscellaneous useful routines Miscellaneous useful information BBC BASIC & in-line assembler