On-Board Communication via CAN without transceiver

[MissionYE]

Two CANs on the same board. Can I connect CAN1TX to CAN2RX and CAN1RX to CAN2TX?

[Javier1]

Never tried it myself but why not, try with some diodes and a pullup resistor.

The canbus line needs to be pulledup high when idle(pullup resistor, if your chips logic is 3v3, use 3v3 for the pullup)

The Rx and TX need to be conneted together, so we need a diode to avoid Tx lines to spill their voltage and mess with the bus.

https://e2e.ti.com/support/microcontrollers/c2000-microcontrollers-group/c2000/f/c2000-microcontrollers-forum/605836/tms320f28035-can-bus-without-transceivers-using-ecan

[MissionYE]

Thanks

[Tesla DeLorean]

Keil​ has white papers on this and on STM3

[Didier_G]

The approach looks valid for low bitrates only.

[Tesla DeLorean]

Bob suggests it's certainly viable to 500 Kbps on small boards

https://www.keil.com/appnotes/files/apnt_236.pdf

Similar mechanics could be applied to UART single wire bus.

[Didier_G]

This speed is far from being confirmed and this trick is probably not viable in production (automotive grade, noise immunity, etc ...).

Schottky diodes with fast transient response are required. The pull-up value has probably to be decreased if the number of controllers increases, for smart edges.

[MissionYE]

Best regards-Amin