On Sun, Jan 31, 2021 at 5:05 PM Fritz Mueller via cctalk < cctalk@classiccmp.org> wrote:
> Hi Josh, > > ZAP is effectively reset for the micro-architecture, forcing the ucode > address to known/initial value. It has multiple sources throughout the > processor, including tendrils into some of trap handling hardware. (Caveat: > my experience is based off extensive work with the '11/45, but the > micro-architecture as I understand it for the '11/70 is quite similar.) > Yeah, ZAP seems to be the entry point at power-up as well as for trap handling. > For the '45, there was a very handy "KB11-A,D Maintenance Manual", which > explained the logic of such internal signals and the board by board > internal operation of the CPU to a very useful level of detail; I'm sure > similar is available for the KB11-B,C? It's worth a read through if you > haven't already, though its quite a bit to take in. > Yes, there's a similar doc. The engineering drawings include the flow diagrams for the microcode, and the Processor Manual ( http://bitsavers.org/pdf/dec/pdp11/1170/EK-KB11C-TM-001_1170procMan.pdf) goes into details on the rest. I started digesting all of this last night, it's going to take awhile :). > > I would imagine the next step would be to throw the RAC board out on > extenders, verify that ZAP is asserted, and if so pursue the driving source. > Yeah. I want to get the fans installed and then go triple-check all the power signals and get the voltages dialed in nicely. But then things come out on extenders :). > > Do you know if you have a KB11-B or C? > It's a KB11-C. > Happy hunting! > Thanks, it'll be interesting for sure. - Josh > --FritzM. > > >
