Reading HP67 ROMs

[teenix]

Hi all,

I removed the faulty 1818-0232 ROM/RAM from the CPU board and I programmed a microcontroller to operate as a 1818-0232 ROM only. Then I hooked it up to the 67 CPU board and monitored the instruction flow.

At address $0068 the code jumps to a subroutine in this ROM at address $0FC6 for 5 instructions then returns and this is exactly what happened.

The LED display lights up incorrectly, but this is because the RAM in both the 1818-0231 and 1818-0232 chips is faulty. I could not read or write anything in these using my ROM reader. The display mode is defaulting to SCI 0 which is what it should do.

The processor is also programmed to operate as a ROM 0 IC, so the next stage is to make sure it decodes the Is bus and outputs correct LED display information to the anode driver.

cheers

Tony