PET 4032 keyboard scanning problem / was Re: Anyone have an

On 4/9/10, Tony Duell <ard at p850ug1.demon.co.uk> wrote: They are... http://www.zimmers.net/anonftp/pub/cbm/firmware/computers/pet/index.html An 80C52 or ATmega8515 (depending on what your preferred architecture is) has at least 24 I/O lines and can be easily interfaced to via serial port. A slightly more complex way of doing it might be to gang a pair of '595s together for a 16-bit SPI-interfaced port (3 wires for clock, data, and latch) to drive the address bus off the 6502 socket then generate _R/W, Phi2, etc, and read or write what's at that address from some 8-bit bidirectional port your tester happens to have (doing read-only tests could result in a simpler tester). I myself have been doing exactly these sorts of tests recently on a pile of 1977-1978-era Static PET boards with a Fluke 9010A and 6502 pod. I've even identified three bad 6540 ROM chips (out of 16 or so tested) and one bad 2316. The 2316 was 100% bad (all reads were zero), but the 6540s were about 1% bad - I was surprised at that. Of course with a tester that's as sophisticated as a Fluke 9010A, you could probably write a Fluke program to set up the PIA to scan the keyboard matrix and test that aspect of the circuit independently of any ROM tests. If you don't already have a Fluke + 6502 pod lying around and don't have enough 6502 machines to repair to justify the investment, it shouldn't be too hard to make a microcontroller-based 6502 memory map tester, even from something like an Arduino (for those that don't want to roll their own stuff 100% from scratch). -ethan