Sinclair ZX80 / ZX81 / Z88 Forums

To give this forum some traffic I have set up this thread.

If you have a question for me just ask here and I will give an answer.
This can be anything about coding on the ZX81 but also a bit more personal.

I will start with the first question and the answer and then it is up to you.

Rules:
no next question before I have answered the latest
you can ask a new question after someone else made a question (no 2 in a row)

How did you start coding on the ZX81?

I played on a ZX81 in the '80s but never had one.

I made a port of my ZX Spectrum game SHOGUN in 2011.
It was a hires game and while searching the net I found a routine to code a 1K hires demo.
This demo gave me the idea to start coding a full game in just 1K.

The fact that you only have 1K (screen included) is to me the sport to make a game fit in 1K.
After the 81 hires games I now code 1K lowres games.

I am now also doing some projects on the ZX Spectrum.

I don't have an immediate question, but thanks for starting the thread!

What is your most favorite instruction/feature when coding on the Z80 in assembly?

mrtinb wrote: ↑Wed Nov 08, 2023 6:57 am What is your most favorite instruction/feature when coding on the Z80 in assembly?

On the ZX81 that is the feature that code can be executed during line display, the call to upper memory.

In hires I use this mainly to prevent display of a user defined character.

In lowres it is used by the system with the HALT, but I use opcodes like LD B,B etc.... to show a space on the screen, but I can store information about that screenposition on the screen. My latest program Game of Life stores the number of adjacent colonies in that space. Snakebingo keeps the track of the tail in it, Minesweeper the number of mines and Pathmaze the paths available. Kman keeps the data of what is eaten, a dot or a powerdot.

More games use the trick.

Have you ever tried programming for the Lambda 8300? It has base memory of 2k, but with a different charset, and no hires or pseudo-hires.

NOT YOUR TURN, mrtinb

Sorry, I didn't see the last rule.

dr beep wrote: ↑Tue Nov 07, 2023 8:09 pm I played on a ZX81 in the '80s but never had one.

Did you use a Zeddy emulator or a ZX81 of someone else?