24 Jun
2016
24 Jun
'16
10:42 p.m.
On Fri, Jun 24, 2016 at 7:41 PM, Fritz Mueller <fritzm at fritzm.org> wrote:
Thanks for the info, Don -- learning a lot about this
stuff as I go...
I had wondered if the part might have been a mask ROM rather than a PROM.
And wrt. timing, I was certainly mistaken to call the nominal interval
between the clock pulses a microcycle.
So after staring at the flows and prints a little more closely, it looks
to me now like the IR will be latched at FET.10 t6 (which is really IRD.00
t1?) then there is the rest of intervening IRD.00 during which time control
signals can propagate to and through decode logic and the subsidiary ROM
and ALU, then the ALU results are latched into the shifter at EXC.80 t2 or
EXC.90 t2. So that's a solid 150ns there minimally?
From the prints, it looks like this is an open-collector part -- I don't
see it called out, but the chip select is wired active and I can't see that
the outputs have any other drivers.
So that's good news for repairing my board! Which brings on the next
question: do folks here have a recommendation for a good programmer to try
and track down on eBay for programming these sorts of parts?
A Data-I/O 29A or 29B will do the job nicely.
- Josh
cheers,
--FritzM.
On 06/24/2016 06:28 PM, Don North wrote:
Almost 100% certainty the part already there is a
small bipolar TTL PROM.
What would you think it otherwise might be?
For a lot of these logic replacement applications DEC used the open
collector version, but it might be tristate variation. Check schematic.
Also, the microcycle on the 11/45 (and 11/70 for that matter, basically
the same design) is 150ns, not 30ns.
There are various clock timing pulses (tp1, tp2, etc) but the datapath /
control unit microcycle is 150ns.