Thursday, 11 May 2017

ZX80 Keyboard Overlays

When the ZX80 was released in 1980, it came with a version of BASIC in a 4K ROM chip, known as 4K BASIC. Note this has nothing to do with RAM (the ZX80 has 1K, upgradeable to 16K), it is the size of the ROM chip.
When the ZX81 was released in 1981, Sinclair offered ZX80 owners the option to upgrade to the same BASIC as the ZX81. The upgrade kit consisted of a new 8K ROM chip (so this version is known as 8K BASIC), a ZX81 user manual and a keyboard overlay.
The overlay is the same as the ZX81 keyboard, and contains many new keywords, and moves some of the existing keywords around. So if you want to use 8K BASIC, you really need the new style keyboard. Software for the 4K ZX80 was not compatible with the 8K  BASIC, but an 8K BASIC ZX80 could load some ZX81 software (anything which didn't use the 'slow' mode display).
To use these, you opened up your ZX80, ideally without snapping the plastic or losing the rivets, although that is tricky.
The new 8K ROM replaces the old 4K ROM, and the keyboard overlay sits on top of the original.
You then end up with a much better and more capable version of BASIC, but a ZX80 that just looks wrong.
This is wrong, do not do this to your ZX80! You don't see many ZX80's like this these days, as most people prefer the classic look with the blue keyboard.
With the Minstrel ZX80 clones, I have been using ZX81 replacement membranes.
These only come in the version with the grey keys and 8K BASIC keywords.
For the ZX80 builds, I got some overlays printed which stick over the ZX81 membrane to make it look like a ZX80.
You then get the same problem, if you want to use the 8K BASIC, you can't use the nice blue keys, you need to use the ZX81 grey keys, so when I have been building 8K BASIC versions, I used the ZX81 black and grey colour schemes.
I have now designed some new membrane overlays, with all the new 8K BASIC keywords, but in the colour scheme of the original 4K BASIC keyboard.
This now gives you the choice of 4K or 8K BASIC, but keeping the look of the original ZX80. This can be stuck over a ZX81 replacement membrane to make a ZX80 8K BASIC keyboard.
This contains all the keyboard markings of the ZX81, but with the yellow, blue and white colour scheme of the ZX80 keyboard.
You can even fit one to your original ZX80 so you can use 8K BASIC without the embarrassment of having a ZX81 style keyboard fitted.
However, I wouldn't recommend modifying an original ZX80, you should buy a Minstrel clone instead!
The clone kits are now available with a set of overlays for either 4K or 8K BASIC, see my Tindie Store for more options.
I have also added complete built units to the Tindie store, so you can buy a white ZX81 cased ZX80, now with a choice of keyboard overlays.

My thanks once again to Grant Searle, these were adapted from his ZX81 overlay artwork.

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