The TomTom data connector uses a non-standard 2.5mm audio style jack that has four poles on the inside and two around the outer sheath. I have been unable to find a convenient source for the connectors so will remove and replace with a cable to mate with a Digilent PmodRS232 adapter to perform 3.3V TTL to RS232 conversion during debugging. I’ve done some work with a scope and resistors to determine the pin functions for at least the pins I require. The connector viewed from the top of the PCB looks like this:
Pin functions were determined as:
1 = RX data in for UART ttySAC0, default rate = 115200, 3.3V TTL.
2 = Power output for accessory, I tested sourcing 100mA will no ill effects on unit.
3 = TX data out for UART ttySAC0, default rate = 115200, 3.3V TTL.
4 = Measured 1.4V output, most probably an audio line output.
5 = When connected to ground via a 1K resistor the unit reports an external line input, so presuably that’s what it is.
6 = Ground.
7 = Function unknown but when connected to ground via a 10K resistor it caused an immediate shutdown of unit.