On 06/24/2016 06:36 PM, Fritz Mueller wrote:
Hi All,
In bringing up and debugging my PDP 11/45, I found that
one of my GRA (M8101) spares has a failed ALU subsidiary
ROM. It's a pretty standard little 32x8 ROM in a 16-pin
DIP, and the truth table is in the 11/45 print set.
I wonder what the replacement options are for parts like
these? In particular, given the 30ns micro-cycle on the
KB11-A, and the fact that the propagation time for the ALU
downstream of this is roughly 20ns on its own, I'd be
worried that an off-the-shelf bipolar PROM might be too
slow here.
I'm still a little slow on reading the microcode flows, so
its not clear to me exactly how many micro-cycles there
are on the critical path for the E-class instructions
where this ROM is used. Maybe its not an issue.
Anybody every try replacing one of these with a bipolar
PROM? Any other suggestions for how to repair parts like
these?
Well, you could use a scope to find out what the good ROMS
do for access time.
Jon