> David Shoemaker wrote:
>
> !Latch2 & !Latch 3 are not being set by the ls74 decoder at J7 as a result the
> X data is not being passed onto the AV Genrator. But the two unused lines are
> toggling. The ls74 tests good. So it looks like the inputs to it are bad
> this is state 0-2 and state 3 from the state machine control.
Isn't J7 an LS42?
If you look at the opcode process sheet (the one you retyped) you can see the
steps that each instruction goes through to get the instruction done. With
it you should be able to 'know' what ST0-3 should be. If the inputs to the
LS42 are okay and they are actually being decoded correctly then I would suspect
either the PROM or the LS74 at L7. The LS74 @ L7 simply holds the last ST0-3 on
the SM PROM so that it knows where it is going.
jess
Received on Mon Aug 30 23:42:48 1999
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