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Quicksilva Character Board
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The QS Character Board was produced by Quicksilva.
It was designed to plug into the QS Motherboard, also produced by Quicksila.

This board operated by overriding access to the character bitmaps held in the ZX81 ROM with 1K of RAM, thereby allowing alternate, user defined character patterns to be displayed.

Several Quicksilva games supported the QS Character Board, namely
- QS Asteroids,
- QS Invaders,
- QS Scramble and
- Cosmic Guerilla.

Hewson Consultants' Puckman and
Artic Computing's ZX-Forth also support the QS Character Board.


Technical details:

The RAM of the QS Character Board is accessed within the memory map at $8400-$87FF. The RAM is always accessible for reading and writing, but the onboard switch determines whether the pixel patterns are fetched from the RAM or from the ZX81 ROM.

Locations $8400-$85FF hold the bitmaps for the normal 64 characters, and locations $8600-$87FF hold the bitmaps for the inverse characters. The ZX81 display hardware automatically inverts the pixel characters for any of the ‘inverse’ characters. This means that the pixel patterns must be stored in RAM in inverted form such that the ZX81 display hardware inverts them back to non-inverted form.

The QS Character Board used a DIL switch to enable/disable its operation. Programs could not read the state of this switch
and so either just had to assume the board was present or would prompt the user to enable it. A program could attempt to
determine whether RAM existed between $8400-$87FF but couldn't guarantee that this was due to a QS Character Board instead of
a 64K RAM pack.

Games, such as QS Scramble, would load in two parts. The first sets up the QS character pixel patterns in RAM. It then puts up a message to the user informing them to ‘switch on’ the character board. Then after a few seconds, it would load the second part, which contained the actual game.

The board also had 4 DIL switches, one of them was to enable the custom charatcer set to be displayed and the other 3 to modify the access timing. The manual speaks of different settings for ZX81 slow mode and ZX80(ZX81 in fast mode.

[partly based on the description for the CHROMA81 interface by Paul Farrow]