Hardware Components Software Running Unix

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.

M8182

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:

This is the top view of the M7195. The stickers on the EPROMs are nearly worn off.

M7195-FA

This is the bottom view of the end of the M7195, with the modification to disable the RAM circled in red.

M7195-FA Back

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.

M7195-FA Modification

References


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