Hi, I use a device with ADM2582EBRWZ tranceiver. It connects to the other device using RS-485 mode. The device sends request to remote device and receives answer. In some cases voltage level in A and B lines becames less than ground potential (ground in bus side). Then signal in RxD pin has fixed level and receiving fails.
Below depicted oscillogram - yellow line is signal in differential pair (A or B) with respect bus ground, blue - signal in RxD pin with respect digital ground (grounds are connected between themselves because measurement). First frame (left side of image) - is ADM2582EBRWZ tranceiver transmitting, then follows answer from remote device (right side of image). The answer pass on RxD pin but then interrupts and RxD sets high level.
Meanwhile differential signal between A and B lines is nice:
- Tranceiver has terminating resistor 120 Ohm and pull resistors 1k to power of tranceiver and bus ground.
- A/B and Z/Y lines united in one RS-485 network.
- The problem also exists in RS422 mode.
What could be the problem?