Program counter + instruction buffer is complete!

After about 6 hours working today, I managed to get the remainder of the program counter + instruction buffer complete.  Here's what the completed setup looks like:

 The leftmost board is the control unit, the center board is the program counter, and the rightmost board is the custom PCB I built that houses the instruction buffers.

I ended up spending about 2 of the 6 hours trying in vain to build a reliable cable to connect these two boards using standard SIP sockets and ribbon cable.  But it was all just too flaky and unreliable so I decided to brute-force it and just graft a piece of old perfboard between the two SIP headers, then wire-wrap and solder the interconnect.  It's not pretty, but it's definitely reliable, when is crucial when it comes to the more complex parts of the system.  I don't want to be chasing down a loose wire in a cable while I'm trying to debug the complex inner workings of the various execution units!

Here's how it looks with all the logic analyzer probes attached.

Success!  My test pattern appears properly on the analyzer.  I also double-checked the 40-pin sockets behind the buffers and found (and fixed) one short, but aside from that everything was perfect!

Now onward to the shift/jump unit.  I've got some new ideas about how to implement it that will take  most advantage of single-sided PCB etching without having to resort to a lot of convoluted, complex extra wiring.  More on that as I start getting the board designs finished...