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Welcome to the CBM-PLA Project Page! The PLA chips, or Programmed Logic Array, used in some CBM machines tend to go bad after a while. While not exactly the same, a common EPROM chip can be programmed to act like these PLA chips but due to a different pinout are not direct replacements. The EPROM pinout must be adapted, which is where this adapter comes in.
The design for this PLA adapter came from http://www.vic20.de/html/eprom_pla_8296_und_c64.html. I could only find a picture of the board, no gerbers, or CAD versions, or any source to purchase them, so I decided to re-create and slightly reduce the size of the board using Kicad.
This board can be used in any of the following:
You must download and burn the appropriate EPROM binary file (from the github repository) onto a 27C512 EPROM or equivilent. The original page recommends an EPROM with a rated speed of 25ns (nanosecond), but says it should also work with speeds up to 255ns. I recommend you use the fastest speed if possible.
Working!
Boards have been made and the design has been verified!
Kicad files, gerbers, and eprom binaries are available on Github: https://github.com/sjgray/CBM-PLA
Page Created: Apr 26/2022. Last updated: Apr 26/2022, 4:30pm EST
Send comments or feedback to Steve Gray(sjgray@rogers.com)