I'm trying to get my M9312 to work with my PDP-11/05 but there appears to be something wrong with the board. By itself, if I plug the M9312 into the standard bus terminator slot, nothing works. The system wont auto-boot the console emulator and I get a bus error trying to read the ROM using the front-panel (address 165XXX).
So I broke out the scope and started to check the basics; e.g. was the basic UNIBUS read cycle being recognized. Almost by chance I stumbled across a curious behavior: If I connect the scope ground--not the input, just the ground--to one of the inputs of the MSYN NOR bus receiver, the board magically comes to life. I can read the ROM and run the console emulator.
The circuit in question is here:
The point at which I attach the ground is E19 PIN 10 / E28 PIN 7 (either will do). No other points on those two gates seem to provoke the correct behavior, including E28 PIN 6 (BUS MSYN L) or E19 PIN 11 (BUS C1 L).
My non-EE conclusion is that one of the two gates is bad. Question is which one? Anyone have any insights?
Thanks,
--Jay
So I broke out the scope and started to check the basics; e.g. was the basic UNIBUS read cycle being recognized. Almost by chance I stumbled across a curious behavior: If I connect the scope ground--not the input, just the ground--to one of the inputs of the MSYN NOR bus receiver, the board magically comes to life. I can read the ROM and run the console emulator.
The circuit in question is here:
The point at which I attach the ground is E19 PIN 10 / E28 PIN 7 (either will do). No other points on those two gates seem to provoke the correct behavior, including E28 PIN 6 (BUS MSYN L) or E19 PIN 11 (BUS C1 L).
My non-EE conclusion is that one of the two gates is bad. Question is which one? Anyone have any insights?
Thanks,
--Jay