SLLS983J June 2009 – September 2019 ISO1050
TXD (Input) and RXD (Output):
VCC1 for the isolated digital input and output side of the device maybe supplied by a 3.3-V or 5-V supply and thus the digital inputs and outputs are 3.3-V and 5-V compatible.
TXD is very weakly internally pulled up to VCC1. An external pullup resistor should be used to make sure that TXD is biased to recessive (high) level to avoid issues on the bus if the microprocessor doesn't control the pin and TXD floats. TXD pullup strength and CAN bit timing require special consideration when the device is used with an open-drain TXD output on the CAN controller of the microprocessor. An adequate external pullup resistor must be used to ensure that the TXD output of the microprocessor maintains adequate bit timing input to the input on the transceiver.