Still looking at the ROMs, seeing as Test ROM works. Guidance keeps me looking at this circuit of 139 and 138 chips, while I wait for a ROM board to help with testing.
I thought I would do a table of some quick Chip Enable and Output Enable readings, so I have it somewhere
I guess chips are meant to always be enabled and then pin 20 should pulse with data as the output pins are enabled to push data out. The probe "pulse" light does flash, even when the H light is constantly lit, unlike some lines that flash both H and L and pulse. If its pulsing, Id have expected to see both H/L flashing and pulse...(PROBE LINK)
I thought I would do a table of some quick Chip Enable and Output Enable readings, so I have it somewhere
I guess chips are meant to always be enabled and then pin 20 should pulse with data as the output pins are enabled to push data out. The probe "pulse" light does flash, even when the H light is constantly lit, unlike some lines that flash both H and L and pulse. If its pulsing, Id have expected to see both H/L flashing and pulse...(PROBE LINK)
ROM | CE (PIN 18) | CO (PIN 20) |
|---|---|---|
C | L | H (but pulse light on probe) |
D | L | H/L (pulse light on probe) |
E | L | H (pulse light on probe) |
F | L | H (pulse light on probe) |
G | L | H/L (pulse light on probe) |




