PDP-11/05 microcode dump?

Noel Chiappa jnc at mercury.lcs.mit.edu
Sat May 7 11:20:06 CDT 2016

    > From: Mattis Lind

    > Now I am convinced that if I program a new A04A2 PROM the machine
    > should behave much better.

Indeed! I have annotated the PROM tables on the Computer History wiki page
with the function of each, and that PROM is the high part of the 'next
microinstruction' field, so if it's bad, the computer will be acting very
strangely indeed! :-)

    > The failing chip was yet another NS chip in plastic

Can you see the type? I'd like to add to the page lists of all the alternate
chip types DEC used in place of the Intersil chips specified in the drawings.

    >> the 'F' etch rev has one less PROM chip than the 'E' etch rev, but I
    >> suspect .. that it's not a micro-program chip, though

My guess was correct; the missing chip is the one I called "Internal
interrupt acknowledge"; it was replaced with a 74154 4->16 demux.


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