3.line connection: 9 lines total
apple --- pc
GND pin 25 as GND
PB0 pin 2 as apple side handshake in (apple -> pc);data bit 0
PB1 pin 3 apple input data bit 1
PB2 pin 4 apple input data bit 2
GC0 pin 5 as apple side handshake in (pc -> apple)
AN0 pin 15 apple output data bit 0
AN1 pin 13 apple output data bit 1
AN2 pin 12 apple output data bit 2
AN3 pin 10 apple side handshake out