REM Line length

[Vorticon]

Hello.
I've recently dug up my TS-1000 computer from storage and have decided to teach myself Z80 assembly on it using Toni Baker's Mastering Machine Code on Your ZX 81 book. I already have substantial assembly language experience with the TMS9900 and 8080 CPUs on other retro platforms so I'm not a total beginner, but doing assembly on the Zeddy hardware (not emulation) appears to be a particular form of masochism
Nonetheless, I am making heady progress. The book, although advertised as a complete beginner's book, is rather amateurish and leaves a lot of important details. For example, it presents several ways to enter and save machine language code using either REM statements or arrays along with example code, but does not explain what all those mysterious address used are and how the code itself works. I figured it out after gathering scattered information from various sources, but I can see how this would be a very difficult task for a newcomer. And don't get me started about the reference tables at the end of the book which use all sorts of notations nowhere explained in the book. I might as well have been staring at an Aztec codex...

But enough whining. I do have a question: How many characters can be stored in a single REM statement?

[1024MAK]

There is the assumption that an owner has read and understood the Sinclair ZX81 BASIC Programming manual (this was supplied as standard with all ZX81 computers, I don’t know if a similar book was supplied with TS1000 or TS1500 computers or other official ‘clones’).

Despite it’s title, the manual goes further than just the normal introduction to BASIC, in chapter 27 it explains the organisation of memory. Essential if you are programming in assembly language. As is chapter 28, where the system variables are detailed.

This manual is available on line if you search for it.
HTML version
PDF version

As is an error corrected HTML of Toni Baker's Mastering Machine Code on Your ZX81 book. Link

This web page is also very useful

Anyway to answer you question, any BASIC line, including a REM line, uses two bytes for the length, which includes the NEWLINE (end of line) marker.

The practical problem is that of either the actual available memory, or how slow the edit line gets as the line length gets longer…

[1024MAK]

Here’s an example showing how long I made a REM line before I got bored…

If you poke the BASIC program area and change the line length, you can ‘merge’ two consecutive BASIC lines into one longer line. But you must correctly update the line length.

Mark

[Vorticon]

Yes I have read the user's manual for the TS1000 which is where I found out about the way program lines are represented in memory. But nowhere was there a mention of how long a program line can be. Most retro computers limit you to 256 characters. Is that the case here or one can just keep going until the screen is filled up?

[roganjosh]

Most retro computers limit you to 256 characters. Is that the case here or one can just keep going until the screen is filled up?

You can have a REM statement that fills up most of the available RAM. It'd obviously be tedious to type in though. I wrote a little assembler program a while ago where you're prompted for the number of reserved bytes you want and it produces a REM statement with line number '0' (which normally won't clash with existing lines and also is relatively safe from deletion) containing the required space. The source code is attached along with an assembled binary. It was written to be used under EightyOne so you load the binary in as a block at address 30000 and do a "RAND USR 30000" to start it. The assembly address was chosen arbitrarily. Obviously don't have the REM space ploughing into the machine code routine. You can also enter a hex value if the hex digits are preceded by a '$'.

Alan

[Moggy]

Just about every toolkit for the 81 included a REM extender of some sort I seem to recall.
I have the Delphic toolkit in EPROM form on a Hunter EPROM board with which I premade a lot of REMs for uses various It's on the forum somewhere as far as I know.

[1024MAK]

Yes I have read the user's manual for the TS1000 which is where I found out about the way program lines are represented in memory. But nowhere was there a mention of how long a program line can be. Most retro computers limit you to 256 characters. Is that the case here or one can just keep going until the screen is filled up?

Because a program line uses two bytes for the length, any program line can be a significant portion of the available RAM. So far in excess of 256 bytes. I say bytes rather than characters, because keywords, such as REM are single byte tokens. And numbers are followed by hidden five byte floating point representations. But obviously it can’t be 64k bytes long, as BASIC can’t use all of the Z80 address space.

Mark

[Vorticon]

You can have a REM statement that fills up most of the available RAM. It'd obviously be tedious to type in though. I wrote a little assembler program a while ago where you're prompted for the number of reserved bytes you want and it produces a REM statement with line number '0' (which normally won't clash with existing lines and also is relatively safe from deletion) containing the required space. The source code is attached along with an assembled binary. It was written to be used under EightyOne so you load the binary in as a block at address 30000 and do a "RAND USR 30000" to start it. The assembly address was chosen arbitrarily. Obviously don't have the REM space ploughing into the machine code routine. You can also enter a hex value if the hex digits are preceded by a '$'.

Alan

Thank you! I'll see if I can adapt it to run on real hardware using er... a REM statement
I have to admit the Zeddy is a very peculiar machine, hence the attraction.

[kmurta]

... but doing assembly on the Zeddy hardware (not emulation) appears to be a particular form of masochism

I recommend using ZX Assembler 2 to minimize difficulties, although it has limitations if you are developing large programs. The ideal would be to have 8KB of RAM between 8192 and 16393 for the assembler and leave the 16Kb of RAM exclusively for the program under development. But with only 16Kb you will still have approximately 8Kb for your program, which I believe is enough for most needs. Take a look:

ZXASSEM2.zip

(1.48 MiB) Downloaded 83 times

[Vorticon]

I recommend using ZX Assembler 2 to minimize difficulties, although it has limitations if you are developing large programs. The ideal would be to have 8KB of RAM between 8192 and 16393 for the assembler and leave the 16Kb of RAM exclusively for the program under development. But with only 16Kb you will still have approximately 8Kb for your program, which I believe is enough for most needs. Take a look:

This is excellent. Thank you.
I have a ZXpand (original version) which should make it easy to transfer the program to the computer. I'll probably also make a copy on physical tape in case my ZXpand fails.