Compatibility between ZX80 and ZX81?

[Paul Panks]

How compatible is the ZX80 with the ZX81?

Paul

[yerzmyey]

I'm sure there are much more wise guys here, than me, but as far as know the comps are not actually compatible.
I mean in way of saving files. Basic by itself it's kinda similar.
I even tried to load (on emul) a file from ZX80. It hang up.

[BrunoFlorindo]

The BASIC is different on each one. I've been reading books and magazines with BASIC listings, and for some time each program had two versions, one for each computer. Some people upgraded their ZX80 to make it better (replaced the rom, etc), but I can't remember if it could become a fully-working ZX81 after the upgrade.

Read about some of the differences here:

http://computermuseum.50megs.com/brands/zx81.htm

It's been a busy week and I can't think straight right now (too tired), but if I can find books or magazines with some examples, I will let you know. You could also take a look at the manuals for both computers:

http://www.xs4all.nl/~fjkraan/comp/zx80/om/zx80om.html
http://www.zx81kit.com/online_zx81_manual.htm

[siggi]

If you replace the ZX80 by a ZX81 rom you get a ZX81, which runs only in FAST mode. There was an hardware add-on (NMI generator) to run this ZX80 with ZX81-rom also in slow mode. And there was a new keyboard foil to be glued on the ZX80 keyboard to have the new ZX81 keywords available.

Siggi

[yerzmyey]

I wonder - I also previously heard that ZX80 worx only in FAST, so that is: nothing actually can move on the screen. Kind of anyway.
And still I have seen several games with moving objects, seemed to be as good as on ZX81 (not many of them 'though).
How is it possible?

[siggi]

The ZX80 runs only in FAST mode. So you have to do some PAUSE to see the result on screen. The other possibilty is to count the executed clock cycles and call the display routine at the right moment
There is AFAIK one ZX80 game (some kind of space invaders), which uses this "trick" to give a stable display like in ZX81 SLOW mode. So what the NMI gernerator does in ZX81 hardware, they did in software on the ZX80.

Siggi