I linked up 2 arduino's to communicate by SPI between them.
I have connected 4 wires between the 2 arduino's CLK, MOSI, MISO and SS except that the SS of the master is going to the external interrupt pin of the slave. the SS pin of the slave is kept unconnected.
The GND's of both the arduino's are connected together.
Except that I have a wierd problem.
When I scope the CLK pin of the SPI bus I find the signal levels have dropped to around 2V and when I disconnect the SPI clk pin from the slave and just scope at the Master end it shows the correct signal levels.
The SPI slave setup code is
void setup (void)
{
// have to send on master in, *slave out*
pinMode(MISO, OUTPUT);
// turn on SPI in slave mode
SPCR |= _BV(SPE);
} // end of setup
inspiration taken from Nick Gammon's code..