Minimum lines for SSP

[HenrikOlsson]

Hi Robert,
The SPI master Clock can run as fast as FOsc/4, ie the same as the instruction clock which, at 64MHz, is 16MHz. ~140times faster than 115kbaud.
The problem is that you're most likely not going to be able to feed the MSSP module with data at fast enough to keep an overall speed anywhere close to 16Mbit. (And it probably won't work reliably over any sort of length of telephone wire....)

The slowest selection for the SPI Clock is FOsc/64 which would be 1MHz in your case - 8.7 times faster than 115kbaud.

/Henrik.

EDIT: Yes for a simple direct Connection they must share the same reference. There are of course things like RS485, optical transmission etc etc but again, for a simple direct Connection they need to share the same GND potential.