What I would do next is grab a logic probe and the
Unibus pinout (for the
terminator slot) and see which grant(s) is being asserted at the
terminator, if any. IIRC, the grants are active _high_, unlike most
Unibus signals. Check the NPG, BG4, BG5, BG6 and BG7 signals at the M9302
terminator
-tony
Finally got a chance to do this; I hooked my logic analyzer to all the
grant signals on the last unibus slot and BG6 is held high constantly,
Rememebr a floating signal will appear as high. Also, if there's a device
that uses BG6 and the BG6 is open between the CPU and that devices,
thenBG6 In on said device will appear high, so the device logic wil
faithfully pass on the grant and set BG6 Out high.
the others seem to be OK. I've confirmed
that these are supposed to be
active high. Now to figure out what's raising the signal...
First check it's not stuck high at the processor end (this could be a
fault with the rbitration logic or similar).
Then I guess you do a half-split. Check it at a slot midway along the
backplane, and move in the apropriate direction until you find what's
causing it.
I disconnected 4-slot the UNIBUS backplane and just stuck the terminator
in A/B of slot 9 of the CPU backplane, and removed the SLU from the SPC
slot. I got the same readings there. I was fairly sure that it's not
the processor -- I make this supposition (and please don't get mad,
Tony :)) because I have a spare 11/40 set and they both exhibit the
exact same behavior when swapped around .
Then I double-checked the wiring for BG6 and the four wires are not
continuous, if I'm reading the wirelist correctly there's supposed to be
a connection from D07F2->F03R2->F03V2->D09M2. The connection between
F03R2 and F03V2 is nonexistent (no evidence of a wire at all). I built
a crude jumper (I need to get a wirewrap tool) and powered it up... and
it works! My God it works! Ha ha ah ahhah a hahahhaa!
Thanks for all the help, Tony (and everyone else too!)
Now to see if I can get the RL02 to boot something. :)
- Josh