Sinclair ZX80 / ZX81 / Z88 Forums

Nice work! I've just read through the first issue. I wonder if you'll run type-in programs (with errors of course!)

I'm afraid you've completely lost me. The Machine Stack is above the BASIC system's GOSUB stack, and I don't see how it can be affected by a standard tape loading operation I'm afraid, since that only loads as far as the top of the Variables area so far as I can see.

When it is just 1K you can use the SP as return to start MC. I haven't tried it to make a BASIC loader that will set SP low on machines with more than 1K. With this method you can load over sysvar and use more without any problems. I think you've just lost me with that. "Use the SP as a return to s...

I am looking at using PRBUFF and MEMBOT (and the two more unused bytes) because I see there 65 lovely bytes that can store program data, "sprite" data etc, for "free" and which are loaded in by the LOAD command, that's why I'm interested in what circumstances might erase or corrupt their contents. F...

Thanks, another question, is it safe to store stuff in the System Variable areas PRBUFF (the printer buffer) and MEMBOT (the calculator memory area) and under what conditions do these get cleared by the ROM? E.g. if I RET from the machine code to BASIC?

Thank you 1024MAK, I'm glad to be here!

And also my brain is starting to frazzle with Z80 machine code...

Thank you everyone for being so helpful. There seems to be a lot of expertise here! I think this is enough to get me started :) Just one more question I'm not clear on, is it possible at all to detect the start of the second user programme execution block, that is (4) in my list, the set of lines be...

I'm still a bit confused. This might be the gap of thirty years :) So far as I can tell from the internet, the sequence appears to go something like this- 1) ISR creates VSync pulse, reads keyboard, updates FRAMES 2) Application execution 3) Display routine (NMI gubbins) 4) Application execution [lo...

Hi dr beep, thank you for your reply. When does FRAMES get updated relative in time to the screen display? I'm hoping to have my code run immediately after the screen has been generated. IIRC, FRAMES update and keyboard reading is done by the maskable interrupt service routine, but I'm having troubl...

Hi, there is not an "introductions" section on this forum so I am saying hello and asking some questions here, if that is okay. I got a ZX81 (16K) in 1981, it was my first computer, when they seemed amazing just to exist at all. I became quite advanced (moderately) at programming machine code at the...