9 Apr
2010
9 Apr
'10
1:50 p.m.
Ethan Dicks wrote:
Interesting, I'm not familiar with the 6540, not sure if there would be
any in this 4032.
On 4/9/10, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
Great, I'll have to cross-check part numbers sometime to see if there are
matches for the ones in the 4032 here.
> Someday I might get back to working on it.
Getting ROM dumps from a
> working
> machine shouldn't be difficult even for the soldered-in ROMs (a little
> PEEKing
> program or such), they may be out on the web already.
They are...
http://www.zimmers.net/anonftp/pub/cbm/firmware/computers/pet/index.html It might be
easiest to desolder the 6502 processor and find some way to
drive the address connections on its PCB position and monitor the data
lines.
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).
I actually use a SWTPC 6800 for this sort of thing on occasion: RS232 serial to
console computer, 6820 PIA lines to DUT, perhaps some intervening hardware
between the PIA lines and DUT. Write a little 6800 assembler program on the
console computer, download it to the 6800 to do DUT control and data capture
and send the data back to the console computer.
It would be nice to build up something a little less cumbersome, however. I
have yet to get around to setting up here for programming modern
microcontrollers. I'll take note of the ATmega8515, I was looking at PICs a
while ago but just wasn't getting enthused about the instruction set.