I have a custom PCB which has a RS485 transceiver chip interfaced to a Nordic microcontroller.
I essentially have a daisy-chained arrangement of RJ-11 ports which are carrying the RS485 A/B signals as shown below. This means that depending on which port is used, the A and B signals can be reversed.
Here is the SP3483 RS485 transceiver chip circuit diagram. I use a Invert signal from the microcontroller GPIO and a XOR gate to handle the RS485 A/B inversion.
Does anyone have ideas on why the RX line is glitching in one of the configurations?
I just found out that other than glitching for the non-inverting case, the RX signal(probed at the DO pin of transceiver) also gives me frame errors, like below: Basically, the RX signal is low instead of being pulled back high after a frame ends, and hence it's recognizing the low signal as an additional byte, which is incorrect.
**To conclude, during idle:
- In the normal A/B scenario, DO pin should go high but its going low.
- But in the inverting configuration(A/B swapped) the DO pin should go low, which it is.**