Sinclair ZX80 / ZX81 / Z88 Forums

I finally got to the bottom of my problem. I looked at the Z80s stack in a monitor and could see the number of items were pushed on at any one time. It would appear that when the ZX81 is in SLOW mode, the stack holds information related to the screen display, because when I went FAST the stack decre...

where do you ldir your program, must be #4009. #676 is after LINERUN so you execute the next BASIC line of the program. OK I see what you are doing with #676 I can also see that I can manipulate NXTLIN to start at any address within the program. In answer to your question, at the moment I am testin...

dr beep wrote: ↑Thu May 21, 2020 7:38 pm Try #676..... I do that in my emulator, but AFTER manually decreasing FRAMES 1x for my games to load.

No, this just crashes the ZX81.

The entry point you are proposing is mid way in the NEXT-LINE routine at #066C
So I can't see how this will work.
Or am I missing something here?

After LDIR just jump to #3E5 See LOAD at #340 and jump at #361. https://k1.spdns.de/Vintage/Sinclair/80/Sinclair%20ZX81/ROMs/zx81%20version%202%20'improved'%20rom%20disassembly%20(Logan%2C%20O'Hara).html #3E5 calls the INITIALIZATION routine. This would destroy all the variables and program. It's l...

A LOAD “” loads data in memory. After the LOAD a simple RET is all that is needed. The LOAD however does this through DISPLAY6, after LDIR your .P from elsewhere over right memory you only need to JP DISPLAY6 ( see ROM-disassembly) NOTE: a simple RET will work for over 99% of the games but not for ...

It is quite cumbersome to add new commands. Modifying the ROM breaks a lot of software. Therefore most hardware extensions are called e.g. with RAND USR 8192. The ROM is full as it is, so adding a new keyword is not possible. But if you insist, the keyword COPY is probably the less used, and you co...

It is quite cumbersome to add new commands. Modifying the ROM breaks a lot of software. Therefore most hardware extensions are called e.g. with RAND USR 8192. The ROM is full as it is, so adding a new keyword is not possible. But if you insist, the keyword COPY is probably the less used, and you co...

Hi I am new to this forum, so first of all hello to all :) I am currently doing a little project where I want to pimp my old ZX81. I am doing the internal 16k static RAM mod, no need for that wobbly blue tacked fizzing RAM pack anymore. I am also replacing the ROM with a 27C512 with a simple latch c...