14 Aug
2009
14 Aug
'09
1:17 p.m.
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, 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.
-tony