TCAN1042-Q1: Does this device need to add pull up or pull down resistors on TX and RX pin?

Hi Sophia,

The device does not require pull-up resistors on either TXD or RXD to function.  There is an internal pull-up already on TXD so that the CAN driver output is recessive if the TXD input is not driven by a controller; external pull-ups could be used if desired to strengthen the bias level in this case (for example, if large leakage currents were expected due to other components on the PCB).  The RXD signal uses a push-pull output stage that does not require a pull-up either, although some users choose to implement one so that the corresponding controller input is at a known logic state in the event that the CAN transceiver is not fully powered.

Some users also choose implement small series resistances on the logic-level IOs.  These are optional as well and can improve signal integrity if the routing distance on the PCB is longer (since they can provide a kind of source-side termination to match the PCB trace impedance).  Series resistances on these lines can also help reduce switching currents, which can be useful if noise coupling onto the power rails is a concern.

Regards,
Max