I'm trying to get 3 PIC18F4321s to communicate using SPI, with one of them in master mode and the other 2 setup as slaves. We first got it working with just 2 devices and no SS (slave select) signal with no issues.
We then added the second device and enabled SS and physically switched the SS wires between 5V and GND and it worked as expected, but when we had the master alternate two output pins between 5V and GND and hooked each up to one of the slaves SS pins, the communication stopped working. We hooked the SS lines up to a scope and could see they were switching the way we expected them to and we had significant delays in to make sure they were never enabled at the same time and that there was time between SS going low and SSPBUF getting loaded with the data.
There doesn't seem to be a difference between physically switching the wires and having the uC do it if there are delays, so the only thing we could think of was that the master couldn't drive enough current to the slaves, but I would think that the SS pins are a pretty high impedance, so I am not sure what could be wrong. Any suggestions would be greatly appreciated.