Wang 600 Potential ROM Fault Log Next
Suggestion of Dead ROM bit
To date it has been possible to demonstrate that:
- the microcode ROM is emitting plausible microcode data
- the machine initialises correctly by loading microcode from address zero
- that some execution sequence follows, but this does not result in correct machine operation
- that single-word microcode show the execution engine is performing at least some functions correctly
This still leaves two general possibilities for the ongoing failure:
- that the ROM is delivering incorrect microcode (perhaps just one incorrect but critical bit)
- that there is a specific fault in the execution engine.
Considering these, it seemed simplest to instrument the entire ROM output and assess if the microcode values were in agreement with the available listings.
Suggestion of ROM Fault
The microcode BI field bit 2 is closely involved in RAM access so a fault in this bit would prevent RAM operations and clearly this would bring down the whole microcode.