On Fri, Jun 24, 2016 at 7:41 PM, Fritz Mueller <fri...@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. >> > >
