Thursday, December 30, 2010

shift/jump unit schematics

I've finished up the draft schematics for the shift/jump unit. I've split the schematics into several sheet, using common nets to link them together. I'll be laying out the PCB for this unit soon (as soon as I finish up drilling and assembly the instruction buffer PCB).

This is (most of) the control logic for the module. Notice that there isn't much complicated logic here -- the first 9 bits of the instruction are reserved for control signals:
  • bits 23 and 22: module select
  • bits 21, 20, 19, 18, 17: instruction (control signals)
  • bits 16 and 15: register bus A select
  • bits 14 and 13: register bus B select
  • bits 12-0: 13 bits of in-instruction data
The output of the modules in this sheet are expanded control signals that determine which of the following tristate buffers are enabled (thus enabling the desired function):

And this beast is a giant multiplexer that determines whether the 13-bit data region of the instruction, or the 16-bit input register, gets sent to the instruction jump bus.

One more tristate controls whether the register control signals may reach the register A/B bus:

And the last sheet simply contains the board's connectors, making it easier to draw the other schematics without having to worry about the specific pinout of the connectors.

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