Hi Julien,
The schematics for the standard six port breakout board 1.2 is online
here, however it is probably easier to look at the device driver file for the breakout board
here, where the pins used for the different lines on each port are specified when the port objects are instantiated, e.g:
self.port_1 = _h.Port(DIO_A='X1', DIO_B='X2' , POW_A='Y7' , POW_B='Y8' , POW_C='Y11', UART=4)
indicating that for port 1 the DIO_A line is pyboard pin X1 etc.
best,
Thomas