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I've had a little more of a play tonight, and I think it's starting to make sense. (Thanks Kevin)

Regardless of the position of the DIP switch, my TWC, upon detecting a vehicle, will start generating a 1kHz 5% Duty Cycle PWM signal ('Digital Comms'). It will generate this for about 3 seconds, and then switch to a duty cycle corresponding with the allocated current i.e. 16% for 10A.

If I switch in a 1.3k resistor when the duty cycle is not 5%, the TWC will switch on an apply power (according to J1172/IEC61851).

If I switch in a 1.3k resistor when the duty cycle is 5%, the TWC will flash red. I suspect it times out if I do not send CAN messages and this timeout is the flashing red. (I don't yet have hardware to sense this and start immediately sending CAN to prove this.)

Hence I suspect Tesla vehicles have the first 3 seconds to establish SWCAN or the session will revert to J1772.

Some third party vehicles will see the 5% duty cycle and switch to Digital Comms (I suspect HomePlug thinking its a DC fast charger) and then timeout.

If you look here : https://github.com/damienmaguire/Tesla- ... gicBoardV4
You will see the schematic for the board on which I implemented swcan. I copied the tesla control pilot circuit exactly even used the very same relay.

Edison wrote: ↑Sat Jun 06, 2020 7:30 am What does IEC61851 define as digital comms? I believe it is ISO 15118-3 HomePlug Green PHY for talking to DC fast chargers.

I'd have to check the current standard but historically it referenced lots different 'digital' protocols which allowed the EVSE to identify the vehicle, etc.

Digital comms have been a feature of the IEC standard for at least a decade (we sold an EVSE controller in 2011 that was 'digital ready').

Edison wrote: ↑Sat Jun 06, 2020 10:15 am Hence I suspect Tesla vehicles have the first 3 seconds to establish SWCAN or the session will revert to J1772.

3 seconds is the ACon timeout which is not Tesla specific. See page 38 in the attached extract from IEC61851-1{ed2.0}