On Sun, Jan 31, 2021 at 7:55 PM Josh Dersch <dersc...@gmail.com> wrote:
> On Sun, Jan 31, 2021 at 7:04 PM Fritz Mueller via cctalk < > cctalk@classiccmp.org> wrote: > >> > 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 :). >> >> Yup -- I'm surprised how picky my '45 is about +5 undervolt; it really >> seems happiest with trimmed up to about 5.1 at the backplane. >> >> Looks like E106 on the RAC (M8123) might be a good place to start >> (drawing RACA, lower left.) >> > > I was just looking in chapter 4 of the processor manual to learn more > about how the processor clocks are generated on the M8139 (TIG) board; on > page II-4-2 (p. 136 in the PDF on Bitsavers) section 4.1.3 it says: > > "The third source of timing [the other two being the crystal clock and a > diagnostic R/C network] is the manually-operated, single-step MAINT STPR > switch S4, located on the maintenance card. This switch is only enabled > when maintenance card switches S2 and S3 are both set to 1." > > Section 4.2.3 confirms this: > > "The maintenance card S2 and S1 switches are both set to 1 to allow single > timing pulses to be generated by MAINT STPR switch S4.... Removing the S2 > or S1 input conditions the MS EN flip-flop to be cleared." > > Well, what's interesting here is that on my system, switch S4 (MAINT STPR) > steps the processor with switches S1 and S2 set to *any* configuration. > Tried it with the other KM11 I have, same behavior. This being the case, I > wonder if the logic that selects the clock source is faulty, and is always > selecting the MAINT STPR input. This would definitely explain the behavior > I'm seeing. I hope the fans arrive tomorrow so I can start debugging this > :). > Ah, and page II-6-20 (p. 178) indicates that when DCLO is asserted, it asserts: "UBCE ROM INIT H - forces the ROM to ZAP.00 (200), and stops and clears the Timing Generator and the Cache timing." I suppose that this is the more likely explanation for the behavior here and that the maintenance card behavior is a side-effect of this. Time to actually probe things, rather than speculating... - Josh > > - Josh > > >> >> cheers, >> --FritzM. >> >> >> >>
