The ISO1044B has internal pull-ups on critical pins which places the device into known states if the pin floats. This internal bias should not be relied upon by design though, especially in noisy environments, but instead should be considered a failsafe protection feature.

When a CAN controller supporting open drain outputs is used, an adequate external pull-up resistor must be used to ensure that the TXD output of the CAN controller maintains adequate bit timing to the input of the CAN transceiver.