[dcbrown]

Dave,

All the stuff I've been doing is bi-directional so I'm constrained by the input delay on paired i/o lines. So yes, if you are only using SDO and don't care about SDI on the SPI interface then I guess you can quick clock just to get the shifted data out. I'd still put a scope on the line. I never got my stuff to work cleanly and looking at the output pulses guessed that it was becuase they looked more like slow rise sine waves than digital data/clock signals.

Might get away with 2t, which is still ~13%/86% levels?, if using schmitt trigger buffers (why did I say schottky?! before) to clean up the pulses.

Line 1-6 are least filtered because they are the external interrupts lines also. So using them up could mean other issues pop up.

I was looking at using a small dual port ram and address blocking. Each co-processor would have their own dual-port ram chip but only part of the address space would be decoded - say 16 bytes. They would have their data lines tied together so the robot controller can access all the data but wouldn't know it was reading chunks from different chips. I was using the analog lines for the interface because that was one of the things I wanted to off-load to another processor anyway. Still bit banging, but bit banging bytes! At least that's the theory.

Bud