accessing multiple MCP23016s

[ecoli-557]

Mr. E (or anyone <grin>-
What is the 'best' way to bus these 23016s off board? I will have 8 of these devices on their own I/O board and looking at the waveforms on 3 of them - the multi-ground cable may not be the best solution.

The leading edge of the waveform rounds off to the falling edge of the pulse. The cable I have selected is instrument-grade but without a foil shield. I am sending +5 with the 2 signals but I do have 3 ground wires and the twist in the cable should have been good enough for the 1 foot of cable between the 8 boards.

The proc is in the middle and 4 boards go out from the left and right.

Should I use a schmidt buffer?

[ecoli-557]

I changed the pullups to 2.2k based on the graph in the I2C specs of 2000. I believe since I am using all MCP23016s and they are 'fast' devices, I should be fine.

The waveforms have a bit of roll-off on the leading edge but look better.

Has anyone used the switched pull up circuit from this refrence?