23 Dec
2005
23 Dec
'05
3:46 a.m.
> Blow a test program into ROM, and let it walk the
memory?
Yeah, but those are both more work than desoldering the RAM and testing
it 'by hand'....
IIRC the NOP instruction is 0x01 - you could knock up something to pull
the bus low apart from D0 when it's /ROMCS is asserted. Some diodes and
an inverter, perhaps.
Then the thing would just madly run NOPS all the time until it fell off
the end of ROM. If it tried to read vectors from ROM it would just jump
to 0x0101.
You should be able to see the address lines doing their thing with a scope
then, albeit briefly.
Gordon.