Hello!
I've recently brought an IMSAI 8080 system back to life. I've successfully gotten it running, but have encountered an odd problem.
When selecting a memory address with the front panel, the inputs in each block of 8 switches are backwards (?) For example, flipping address switch 0 up and hitting examine should should light the LED above it (Address Bus 0). Instead, it lights Address Bus LED 7. This applies to the others: Switch 1 lights LED 6, Switch 2 Lights LED 5, Switch 15 lights LED 8, etc etc. You are still able to deposit bits normally, and they are retained in the location you place them.
Another example: to examine address E901, you would enter E901 (1110 1001 0000 0001) on the switches and hit examine. This doesn't work. Instead, you must enter it backwards on each block of 8 switches: 9E10 (1001 0111 1000 0000), at which point it will show you E901.
I thought the display LEDs might be the problem, so I decided to see if I could access the Disk Controller PROM. Entering the address (E900) in the backwards format and hitting run makes the drive respond, so the address LEDs are correct. It's just the switches that are wrong!
The front panel and MPU are in good order and all the components have been cleaned/reinstalled as per the manual. The memory, serial card and disk controller are also configured properly as per their documentation. I've experimented with various cards removed and it remains the same. Does anyone have any insight into why this might be occurring?
I've recently brought an IMSAI 8080 system back to life. I've successfully gotten it running, but have encountered an odd problem.
When selecting a memory address with the front panel, the inputs in each block of 8 switches are backwards (?) For example, flipping address switch 0 up and hitting examine should should light the LED above it (Address Bus 0). Instead, it lights Address Bus LED 7. This applies to the others: Switch 1 lights LED 6, Switch 2 Lights LED 5, Switch 15 lights LED 8, etc etc. You are still able to deposit bits normally, and they are retained in the location you place them.
Another example: to examine address E901, you would enter E901 (1110 1001 0000 0001) on the switches and hit examine. This doesn't work. Instead, you must enter it backwards on each block of 8 switches: 9E10 (1001 0111 1000 0000), at which point it will show you E901.
I thought the display LEDs might be the problem, so I decided to see if I could access the Disk Controller PROM. Entering the address (E900) in the backwards format and hitting run makes the drive respond, so the address LEDs are correct. It's just the switches that are wrong!
The front panel and MPU are in good order and all the components have been cleaned/reinstalled as per the manual. The memory, serial card and disk controller are also configured properly as per their documentation. I've experimented with various cards removed and it remains the same. Does anyone have any insight into why this might be occurring?