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ortek_service · 29th Mar 2021, 5:18 pm

You'd probably need a tight polling-loop to check row & column lines going low, as might need extra-logic to provide an interrupt. But may not need too many assembly-language instructions instructions in that loop and if mostly 1 or 2 cycles, then may only need to run at a few MHz.

I know you can get DIL40 (but unlikely to be pin compatible with original IC) Atmel ATmega AVR uC's, that will run upto 20MHz and have RISC-like fast instruction set. And I know there are also DIL40 PIC's but may only go upto a few MHz clock speed as I recall there used to be Scenix high-speed ones.
Can also get Silicon Labs enhanced single-cycle C8051's that go upto 50 or 100MHz, ir even a cheap ARM Cortex M0+ etc that go to similar speeds.

The main problem I can see, is that while the processor is outputting (at slower speed?) the looked-up code, it could miss input changes that were being looked-for in a polling loop. So I think it may be best to have a uC that has Input-capture interrupts on all it's I/O pins (assuming that can respond to 10us pulses), for it to detect these, and would also need fairly-fast time to enter the Interrupt Service Routine.

The original IC presumably did it all in Asynchronous logic, so didn't have this issue. So could probably also do it with an FPGA etc, that had enough space for the ROM ASCII etc. look-up table, although these still often require clocking at high rate, unlike many ASIC's.

29th Mar 2021, 5:18 pm	#127
ortek_service Octode Join Date: May 2018 Location: Northampton, Northamptonshire, UK. Posts: 1,440	Re: The Transam Triton Personal Computer You'd probably need a tight polling-loop to check row & column lines going low, as might need extra-logic to provide an interrupt. But may not need too many assembly-language instructions instructions in that loop and if mostly 1 or 2 cycles, then may only need to run at a few MHz. I know you can get DIL40 (but unlikely to be pin compatible with original IC) Atmel ATmega AVR uC's, that will run upto 20MHz and have RISC-like fast instruction set. And I know there are also DIL40 PIC's but may only go upto a few MHz clock speed as I recall there used to be Scenix high-speed ones. Can also get Silicon Labs enhanced single-cycle C8051's that go upto 50 or 100MHz, ir even a cheap ARM Cortex M0+ etc that go to similar speeds. The main problem I can see, is that while the processor is outputting (at slower speed?) the looked-up code, it could miss input changes that were being looked-for in a polling loop. So I think it may be best to have a uC that has Input-capture interrupts on all it's I/O pins (assuming that can respond to 10us pulses), for it to detect these, and would also need fairly-fast time to enter the Interrupt Service Routine. The original IC presumably did it all in Asynchronous logic, so didn't have this issue. So could probably also do it with an FPGA etc, that had enough space for the ROM ASCII etc. look-up table, although these still often require clocking at high rate, unlike many ASIC's.