Using standard PC keyboard with ZX81

[David G]

Has this been discussed before?


Seems like we could use an Arduino or Nano Pi to read a USB/Bluetooth or PS/2 keyboard and generate the correct signals for the 9 pins of the ZX81 keyboard connector. I have sooo many spare keyboards ...

[xelalex]

You could try spectratur: https://codeberg.org/xelalexv/spectratur

It currently supports ZX80/81 and Spectrum, and can be easily extended to support other machines.

[Paul]

If you would like to use a PC Keyboard and maybe a PC Screen, why do you bother to use the original? There are Emulators for that purpose.

[xelalex]

If you would like to use a PC Keyboard and maybe a PC Screen, why do you bother to use the original? There are Emulators for that purpose.

The OP is not about using a screen, just about the keyboard. Adding a decent keyboard to a ZX80/81 or Spectrum makes for quite a pleasant user experience

[Paul]

The OP is not about using a screen, just about the keyboard. Adding a decent keyboard to a ZX80/81 or Spectrum makes for quite a pleasant user experience

I agree.
I just find most PC Keyboards quite inconvenient
For a decent keyboard I use Cherry Keys.

https://forum.tlienhard.com/phpBB3/view ... rry#p35439

I know such a thing exists somewhere for PCs as well. They are just very rare compared to the PC Keyboards I know.
On the other hand I can't imagine what to do with all these keys when only 40 are required

[xelalex]

For a decent keyboard I use Cherry Keys.
I know such a thing exists somewhere for PCs as well. They are just very rare compared to the PC Keyboards I know.

PC keyboards with mechanical switches are actually quite common, I'm typing on one right now (Cherry MX Silent Red). In particular gaming keyboards pretty much always have mechanical switches, be it Cherry or other manufacturers. But the cheap ones are mostly unusable, that's right.

On the other hand I can't imagine what to do with all these keys when only 40 are required

Assign macros

[1024MAK]

The problems with using “IBM” PC keyboards, be they the wired type with 5 pin DIN, 6 pin PS/2 type, USB type or the wireless types are:

• Each has its own internal matrix, so each will have its own ‘ghost’ key combinations. Some of which may affect game play if said game needs multiple keys pressing at once.
• The keyboard layout is different.
• The way that machine code software on the ZX81 (or ZX80, or ZX Spectrum) may scan the (original) keyboard matrix means the interface circuitry has to be more complex than you think.

So, for the later point, to read the keyboard on a ZX81 (or ZX80, or ZX Spectrum), the machine code outputs an 8 bit number on the processor address lines A8 through A15 via an IN instruction. This is the keyboard row. The same IN instruction also reads the five bit column from the keyboard.

Because the row number can be any 8 bit number, any external circuitry must be able to capture this number and then look up to see if any key presses from the PC keyboard matches any of the combinations. Then, before the Z80 reads the columns, it must place the correct 5 bit number on its output lines for the Z80 to read via the keyboard input circuitry (the ULA in the case of the ZX81 or ZX Spectrum). This requires a large amount of processing in a very tight window of time.

Alternatively, instead of trying to have a microcontroller or processor system that is fast enough to do as described in the above paragraph, a electronic matrix using electronic switches can be built. But this obviously requires more hardware.

Simpler systems are possible, but they almost certainly will not support all software.

Mark

[xelalex]

Alternatively, instead of trying to have a microcontroller or processor system that is fast enough to do as described in the above paragraph, a electronic matrix using electronic switches can be built. But this obviously requires more hardware.

This is what spectratur does, using an Arduino Nano (or other) and a Zarlink MT88xx switch matrix. Solves the mentioned problems.