CAN bus voltage bias, related to CanBus
The noise tolerance, and sometimes even operation of the CAN bus depends on
- termination (well known, typically 120 Ohm at/near each end of the differential pair).
- voltage BIAS
Voltage BIAS
Unlike the RS485 transceivers, the CAN transceiver only
- pulls the CANL signal LOW (when actively transmitting)
- pulls the CANH signal HIGH (when actively transmitting)
TJA1050 has weak 25k bias toward 2.5V (VCC/2), but pullup/pulldown would seem desirable:
- CANL: 10k pullup to +5V
- CANH: 10k pulldown to GND
It might work without these pullup/pulldown (it is easy to add externally, and the dash likely has it anyway), but it sounds safe and friendly to just include 10k (or at least a weaker 20k if very cautios).