Tool/software:
Hello,
I have been testing recently developed pcb which included CAN interface with a ISO1042 CAN transceiver. And I cannot manage to drive the bus to the dominant state. The test setup is pictured below.
The microcontroller simply toggles the TX pin every millisecond.
This is what oscilloscope shows:
Purple - CAN2_TX
Blue - CAN_L
Yellow - CAN_H
When TXD is high, all good and the CAN bus in a recessive state as it should be. But when I try to make TXD low look what happens.
The voltage drops to about 1.3 V and then slowly decays to the steady state 0.88V. Because of that the state of the bus never changes.
I was going to blame the internal pull-up, however the datasheet says
which in my understanding means that is shouldn't cause any issues with driving the pin low but only protect in case of floating pin but not prevent it from being driven low.
Some more information that might be useful:
- Resistance between the MCU pin and the transceiver pin is 0.3 Ohms.
- The MCU pin is configured as default PP with no pulls turned off, the GPIO structure looks like this:
What might be the reason for this behaviour and what are the test procedures that might help to understand it?
Thank you,
Ivan
