Processor Module
My PDP-11 system is starting out with an M8192-YB, KDJ11-AB PDP-11/73 processor, with an M7195-FA, MXV11-BF multifunction module. The intent is to load 2.11BSD on the system, which requires a processor with separate instruction and data spaces.
The M8192, shown below, is small, inexpensive and should do the job.
The M7195-FA multifunction board comes with 128 KB of non-parity RAM that does not support block-mode DMA transfers. Unix requires parity support and the the mass storage controller I will be using is an MSCP compatible controller, which uses block-mode DMA. Because of this, the the onboard RAM is pretty much useless. Unfortunately, DEC did not provide an easy way to disable the memory, so DEC MicroNote #19 was written to describe how to do this. The MicroNote lists a couple of ways to make the modification. I chose to cut a solder trace and then add the extra wiring, as described in the MicroNote.
Multifunction Module
The multifunction module is configured to provide the following features for the system:
- Line-Time Clock - set to 60 Hz
- Console - SLU1
- TU58 Interface - SLU0
- MXV11-B2 Diagnostic and Boot ROMs - required for a PDP-11/73 processor
- Diagnostic LEDs
This is the top view of the M7195. The stickers on the EPROMs are nearly worn off.
This is the bottom view of the end of the M7195, with the modification to disable the RAM circled in red.
Here is a closeup of the modification, with the red arrow pointing to the cut in the trace. The blue jumper connects the isolated pin to +5 VDC, which disables the onboard memory. I tried to make the cut in a location that would be easy to fix, in case I ever needed to restore the module to its original operating condition.
References
- DEC MicroNote 19 - Disabling RAM on the MXV11-BF
