Support interfacing to a real Atari ST keyboard (IKBD)

[beeka]

The mega ST / TT keyboard connection is just a UART connection (plus power?) so would it be simple to provide an option to use the spare IO headers (e.g. as intended for the DS2 controller on the MiSTeryShield20k board) to connect a real Atari ST keyboard to the FPGA?

The motivation is that while I love my collection of Atari STs, I'd like to experience the feel of a real Atari keyboard + Mouse with the convenience of the FGPA solution. The alternative is a range of adapters for HDMI, SD Card, Floppy Disk... not to mention the PSU / recapping / "bad" DMA.

As it stands, I would be hoping the Atari-to-USB adapter I made would be compatible, but is yet another device in the loop that just doesn't need to be there.

[harbaum]

That's probably quite simple. The signals are there are the MiSTeryNano actually contains a complete implementation of the ikbd and uses the original serial protocol. You would just have to expose rx and tx to some pins.

I once evaluated the idea of putting the MiSTeryNano inside a real mega keyboard. But these are just too expensive for that and it might be somewhat bad to actually modify one of those rare retro devices for this.

[beeka]

There are people creating drop-in versions of the falcon keyboard (i.e. the same as any normal atari st keyboard) with mechanical switches (and backlighting). Not heard what the price is on those is to know how they compare to an original external keyboard, but there is scope for making a version of such a keyboard PCB that has the FPGA companion board built in to it.

I expect it will be cheaper to find a real atari ST though... and mechanical keys might have the right layout but if the keys are not mushy it probably won't feel quite the same :-)

I'm a software engineer with some experience of embedded systems but FGPA is new to me... I've not dug into the FGPA code or how it interfaces to the companion board to figure out if it would be as simple as routing the IKBD rx/tx signals to the "DS2" I/O connector (would I just need to arrange for an RJ11 connector adapter?)?

BTW: I meant to raise the issue on the MiSTeryNano project... is that a better place for it?

[harbaum]

You need to use level shifters as the FPGAs IOs run at 3.3v but the keyboard communicates at 5v. These can make easily be found at Amazon or Ali. This actually sounds like a nice little experiment for a beginner.

And yes, the misterynano would have been the better place. But it doesn't hurt here ...

[luciust]

A 74HCT245 would be probably a good choice

[harbaum]

Not sure if hct works down to 3.3v. You only need Rx and tx, right? Then any of these cheap i2c level shifters available on Amazon, Ali etc should be sufficient.

[beeka]

It does feel like a suitable introduction... I have previously used kicad to make an IKBD-to-USB adapter. I used a BSS138 to convert the level one way and a couple of resistors to lower the voltage the other way. My first attempt used an IC with bidirectional level conversion but it didn't work in practice... the working solution is actually simpler + cheaper.

I've not gone near FPGA development or even use (preferring the real thing, if only it took up less space). I have only recently ordered a Tang Nano, but looking forward to getting it.

What is the best way to take this forward? Do I design and make an add-on board or a complete companion PCB? Would I need to make a new core with the IKBD changes?

Is there a place to ask the "stupid" questions, or is there a FAQ? I tried the link to Atari Forum but that seems to be down. Is there any design documentation beyond the readme files (e.g. are there any unused pins + conventions on allocation)?

[harbaum]

Feel free to join https://discord.gg/tBJGQXhe6