PB4 - RESET output
PB6 - 1MHz output

PC6 - Enable Tx to MOSI (ISP mode)
PC7 - Enable Tx to DATA (PDI/TPI modes)

PD2 - Rx input
PD3 - Tx output/Z
PD4 - Enable XCK to CLK (PDI mode)
PD5 - XCK output
PD6 - Enable XCK to SCK/CLK (TPI/ISP modes)
PD7 - Enable RESET to RESET (TPI/ISP modes)

PF4 - Vtgt/2 at ADC4

PDI/Tx: PC7=1,PD4=1,PC6=0,PD6=0,PD7=0
PDI/Rx: PC7=0,PD4=1,PC6=0,PD6=0,PD7=0

TPI/Tx: PC7=1,PD6=1,PD7=1,PC6=0,PD4=0
TPI/Rx: PC7=0,PD6=1,PD7=1,PC6=0,PD4=0

ISP: PC6=1,PD6=1,PD7=1,PC7=0,PD4=0
