On 08/04/2017 05:31 PM, Rod Smallwood via cctalk wrote:
Hi Guys
Thanks for the info so far. Well I have moved on.
I now have the minimum configuration.
Programmers console, M8300,M8310,M8320,M8330,M849 and 4k
of core memory.
The M8320 is at the far end of the bus.
Well much as I feared I cant write to memory using Load
Address 0000, set data to 0001, lift DEP.
Then set address to 0000 again and press EXAM. I should
see the contents of MD with the selector switch set to MD.
I don't.
I have checked the correct bus signals go low when the DEP
switch is lifted.
This is so fundamental somebody must have come across it
before.
OK, try reading a few locations and see if you can find a
non-zero one. If so, go back and read it again. If it
still reads the same value, that is a GOOD sign. it means
the write-back after a read worked. If the 2nd read comes
up zero, it means the write-back failed. This would tell
you that the write function of the memory is bad, but the
read function is OK.
If some portion of the memory CAN read/write, then that
indicates that either some decode logic or some select
drivers are not working. If nothing works, then it could be
a configuration issue (the plugged-in memory module is not
set at address zero, for instance) . But, eventually, you
would have to trace it through the prints. Fortunately, the
PDP-8 is not a terribly complex CPU.
Jon
