Troubleshooting
Communications Troubleshooting
Communications Troubleshooting in industrial control systems — covering 5 topic areas in the CurryControls.com controls and automation knowledge hub.
Written guides in this section
Full references, procedures, and diagnostic guides published under Communications Troubleshooting.
Device Times Out
A polled device that answers late or not at all: how to read the driver counters, tell a dead device from a slow one, and find the timeout setting, the bus loading, the radio latency, the duplicate address, or the device that is simply too busy to answer.
9 min readUpdated Sep 5, 2026
Read Works but Write Fails
Polling a device returns good data and writing a setpoint does nothing or returns an exception: a write-protected device, a read-only register, the wrong function code, a wrong address or type, logic that overwrites the value, a security rule, or a local mode.
8 min readUpdated Sep 5, 2026
Wrong Register Data
The poll succeeds and the numbers are nonsense: an offset by one, the wrong table, swapped words in a 32-bit value, a float read as an integer, signed read as unsigned, a scale factor not applied, a stale gateway value, or the wrong unit answering.
8 min readUpdated Sep 5, 2026
Protocol Gateway Stops Passing Data
The gateway is powered and pingable and the data behind it is frozen or gone: the device side failed while the master side answers, a stalled gateway, configuration lost on a power cycle, a stale mapping, or a master polling too fast. Testing each side.
8 min readUpdated Sep 5, 2026
Modbus Device Intermittently Offline
A device that answers most of the time. Termination, bias, timing, and the physical layer details that produce a bus which almost works.
9 min readUpdated Aug 21, 2026
Topics in this area
Modbus Device Intermittently Offline
Framing, timing, addressing, and termination on a bus that mostly works.
Device Times Out
Device Times Out — practical reference notes for controls engineers, integrators, and technicians working with communications troubleshooting.
Read Works But Write Fails
Read Works But Write Fails — practical reference notes for controls engineers, integrators, and technicians working with communications troubleshooting.
Wrong Register Data
Wrong Register Data — practical reference notes for controls engineers, integrators, and technicians working with communications troubleshooting.
Protocol Gateway Stops Passing Data
Protocol Gateway Stops Passing Data — practical reference notes for controls engineers, integrators, and technicians working with communications troubleshooting.
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