ISA Backplane Bridge

The 7 slot ISA backplane has worked well up until now.

However, The project now contains :

  1. CPU card
  2. ROM card
  3. RAM card
  4. Serial card 1
  5. Serial card 2
  6. Programmable Timer Module
  7. Empty

That's 6 of the 7 slots currently being used. This only leaves one remaining slot for the audio card. With the system designed to handle 8 audio cards, and I also have some other cards that will be built, it's now time to address this problem.

Is it time to design my own ISA backplane with more slots? Or is there something I can do short term to get more slots? I could redesign the cpu board to also contain the ram and rom, freeing up two slots. I could redesign the serial i/o board to contain 2 serial ports instead of one, freeing up a slot.

I went with the second option for now, and designed a simple card called a Backplane Bridge to link two of the backplanes together.

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This is just a straight through board allowing two backplanes to be linked together. The ribbon cable is purposely very short to minimize signal loss.

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Now I have 12 ISA slots available for use, giving me five more slots to work with.

The 2nd backplane does not contain any of the power connectors or voltage regulators that the main backplane has since all the power will be bridged over from the main to the secondary backplane. This made populating the 2nd backplane easier as it required less components.

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