HP41C with Rp Pico attached

[blackjetrock]

(06-01-2023 09:41 AM)MeindertKuipers Wrote:  This is a really cool project, and thanks for sharing. I like how you implement the extra display and the HP41 bus tracer. I have implemented an HP41 bus tracer myself and did not expect that a microcontroller would be able to keep up with the HP41 bus speed while dumping the results over USB in real time. But with a 2 core controller things are now different.
The Pico looks like a good candidate for a new generation of HP41 peripherals, although I doubt that it will fit in a module housing with all the level shifters. Also powering the RP2040 from the HP41 battery will be a challenge. But then again I do not mind a box external to the calculator with its own power source.

Thank you.

The extra display was hopefully for a version of this that can run with an HP41C processor PCB and provide a display and keyboard via the Pico. You then have a sort of 'desktop' HP41C. I have a few PCBs with no case and this would allow me to use them. Some of the boards are faulty, as well, so the bus tracing was to help me debug them, maybe. If ICs are broken then I'm hoping to remove the broken IC and emulate that functionality.

If my calculations are correct then the HP41C runs at about 6000 instructions per second on the bus. The bit rate is 56 times that so about 300KHz. The Pico is overclocked to 270MHz so about 800 instructions per clock cycle. There is quite a bit of processing that can be done in 800 instructions. Handling bus traffic is not a problem, therefore, but the emulated data from RAM, ROM, etc has to be presented quickly on the bus so that's a bit more demanding. There are the PIOs available which could probably handle the bus bitstream and hand bus 'words' to the cores. At the moment I'm running one core on the bus decoding and one doing the UI and trace decoding. (And no PIOs).

Yes, I think the Pico or RP2040 could help create quite a few interesting peripherals. There's a Pico with wifi too, although it's not difficult to use a module to do wifi or bluetooth.

The RP2040 is definitely not low power so that will have to be handled with external power or a big battery. I don't think there's any way around that other than power switching circuits that power the RP2040 down completely when not in use.

The RP2040 is very small, but it does need an external flash chip, crystal and some passives, even so, that should fit in a module. Level shifters are needed as the RP2040 is only 5V tolerant. I think the circuit on the prototype PCB I have made could just be fitted in a module. Maybe.

Andrew