Thursday, December 1, 2016

Building a 68000 Single Board Computer - BOM and Preliminary Layout

I spent some time updating the parts list on github, which is available as a spreadsheet and PDF file.

I started a rough layout of the prototype board by printing and cutting out small squares of paper corresponding to each IC and arranging them. I tried to minimize the distance between the chips that interconnect. This gave me the approximate board size needed. I will probably adjust it when I get the proto board as I'm not sure yet if I will put some of the discrete components like pullup resistors on wirewrap sockets or directly on the board.

A 64-pin wirewrap socket is hard to come by, and the lead spacing varies between the different versions of the 68000 chip (e.g. plastic versus ceramic packages). I made a 64-pin wirewrap socket by cutting two 40 pins units with a hack saw.

These are the controls that are planned go on the front of the board:

  • step pushbutton
  • single step/run toggle switch
  • reset button
  • reset/halt LED (red)
  • power LED (green)
  • power toggle switch

I may eventually put the board in a case. If so, I'll either find a commercial case large enough, or maybe 3D print it.

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