Specifications

Appendix C - Testing and Troubleshooting RS-422/485 Systems RS-422 And RS-485 Applications Ebook
Page 92 of 137 Manual Documentation Number: <DocNumber>
www.bb-elec.com/
www.bb-europe.com/
Troubleshooting Checklist
The following checklist may be helpful in eliminating RS-422/485
problems:
1. Get a schematic of each serial port to assist in troubleshooting and repairs.
2. Ensure data signals are within the 200 mV to 6 V range necessary for RS-
422/485 communication.
3. Use a signal ground line to keep common mode voltage within the -7 V to +12
range.
4. Verify that only one RS-485 driver at a time is enabled on the communications
line.
5. Use isolated equipment if possible to avoid problems with different ground
potentials and noise.
6. Add fused output devices to shunting protection to guard against short
circuits.
7. Is the data rate high enough to require termination resistors?
8. If you have added termination resistors, did you check the biasing to ensure
the system would operate?