Saturday, January 29, 2011

shift/jump unit preview

I've decided on the final design for the shift/jump unit.  The unit itself implements four types of instructions:

  • Shift data in register A left one position and write to register B
  • Copy data in register A to register B
  • Jump (based on a few conditions) to an address encoded in the instruction
  • Jump (based on a few conditions) to an address in register A
All four of these instruction types use the same model: read from a bus, do something, then write to another bus.  To simplify construction, I'm building a backplane that makes these buses accessible, and will implement four instruction boards and a control board that plug into it.

The backplane will have SIP sockets, and the risers will have right-angle SIP headers that plug into them.  By expanding the buses from a 40-pin socket to a single row, it will make wiring much easier.

Here's what the backplane currently looks like:

You'll notice that the traces aren't complete -- since I can't do a two-sided board, I'll have to hand-wire some of the more complex bits, such as expanding the 40-pin register A/B bus to the proper SIP sockets.

Once the backplane is complete, it's just a matter of building the various boards one at a time.  Each board will be relatively simple, making building and troubleshooting much easier than trying to build the whole thing in one shot.

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