Troubleshooting RS-485

If the device being synchronized by the RS-485 data does not synchronize within the normal time frame that it is supposed to sync-in, you will need to determine if the problem is related to the master clock (or time server), the RS-485 cable between the master clock and the device or the device itself. Time synchronization of a device may be either intermittent or it may not sync at all. The first thing to determine is whether any other device on the RS-485 bus is synchronized, or are all devices on the bus unsynchronized. If all devices are unsynchronized, the problem is most likely with the master clock or a device loading down the bus. If all other devices are synced, the problem is most likely with that particular device or a cabling issue between this device and the device that is immediately before this device.

Symptom	Action
no system sync	check synchronization of the master clock
no system sync or intermittent	check bus wiring and termination
no synch on one device	check the device, the device before it and wiring

You can further diagnose problems with the RS-485 bus:

Using a TimeTap

Using an oscilloscope