80-Bus News

   

Spring 1985 · Volume 4 · Issue 1
Page 29 of 31

to see if a global variable with the name $MEMRY has been declared. If $MEMRY exists, then L80 will set it to point to the first byte of free memory following the program. The code below gives a simple example of its use and contrasts it with the straight forward approach. 

single assembly  multiple assembly
                 entry $memry   ;Define Entry point
 ......          ......
ld hl,buffer     ld hl,{buffer} ;Point at memry buffer
ld a,(hl)        ld a,(hl)      ;Load byte
ld hl,buffer+128 ld hl,(buffer) ;Point at byte
                                ;128 in buffer
                 ld de,128
                 add hl,de
 ......          ......
 ......          ......
                 $memry equ  $   ;$MEMRY same as BUFFER
buffer equ $     buffer defw 0   ;Define buffer

The basic difference is that ‘buffer’ becomes an indirect reference to the buffer area. There is no real difference in the code when loading HL with a pointer to the base of the buffer area, {one just becomes an indirect load), but the irritation is when you want to load the address of a specific location offset within the buffer area. In the former case the assembler has already done the calculation for you, and you are still only loading HL with an immediate value, while in the latter case you have to explicitly do the calculation in your own code.

Happy hacking!



My dear chap, we seem to have overlooked the fact that ‘C’ is not as difficult as we first thought.

Converting WordStar text files to improve their readability

by P.D.Coker

One of the problems associated with using WordStar is the lack of clear legibility of the text files it produces, unless they are being edited by WordStar itself. This is perfectly all right on most occasions, but there are times, particularly when deciding to delete or dump a lot of text files, when the tedious business of loading them into Wordstar, reading and then exiting, is a bit too much trouble. Using the TYPE command in CP/M gives a visually disturbing result with lots of inverse video characters at the end of words and no nice tidy paragraphs. [Ed. — this is not true of CP/Ms installed with CCPZ, i.e. all Gemini Winchester based systems, and all Gemini CP/Ms of BIOS 3.0 or later.] This WordStar ‘feature’ is also not particularly good if you wish to use PEN on a file originally written using WordStar, since the formatting commands used by WordStar are totally different and a lot more time will have to be spent deleting them and substituting the appropriate commands for PEN.

The strange characters which WordStar inserts are used for justification, tabulating and other formatting functions and they are not normally displayed on the screen when WordStar is in use. Characters such as these have ASCII codes greater than 127 (dec.) and are interpreted by the video controller in an 80-BUS system as inverse (black on white) letters or symbols. Normal text and some other symbols used by WordStar have ASCII values from 0 – 127, and the formatting commands will not interfere with these.

There are two approaches to this problem. One is to use the [Z] option in PIP which sets the parity bit to zero; the following command line will read the text file B:RUBBISH.TXT and produce a cleaned-up version on drive A as GOOD.TXT: 

A>PIP GOOD.TXT=B:RUBBISH.TXT[Z]

This works nicely because the eighth bit is set to 1 in characters beyond 127 and these are the ones which cause the peculiar effects. The drawback to using PIP/[Z] is that you cannot see the edited file unless you call it up by using the TYPE command. There may be various tweaks to the PIP command which will produce a listing on the CON: function — in this case, assigned to the CRT: device, but I haven’t investigated these, and the thought of typing extended PIP command lines (I haven’t got a programmable set of function keys on my machine) didn’t appeal!

Page 29 of 31