Error was: net.wimpi.modbus.ModbusSlaveException Error Code = 4

Setup, Configuration and Use Beginners
1

Hi,

For discrete inputs everything is working fine.

For digital outputs/coils, it’s working .. but getting these error messages.

Getting these errors with Modbus and Beckhoff BC9100 / Digital Output

16:10:24.605 [INFO ] [smarthome.event.ItemCommandEvent ] - Item ‘DO01’ received command ON
16:10:24.669 [INFO ] [arthome.event.ItemStatePredictedEvent] - DO01 predicted to become ON
16:10:24.694 [INFO ] [smarthome.event.ItemStateChangedEvent] - DO01 changed from OFF to ON
16:10:24.935 [WARN ] [ort.modbus.internal.ModbusManagerImpl] - Try 1 out of 3 failed when executing request (BasicModbusWriteCoilRequestBlueprint@89da23[slaveId=1,reference=0,functionCode=WRITE_COIL,bits=SingleBitArray(bit=1),maxTries=3]). Will try again soon. Error was: net.wimpi.modbus.ModbusSlaveException Error Code = 4 [operation ID c2ca648b-fe2c-44d5-a6c4-42099609d1cf]
16:10:25.015 [WARN ] [ort.modbus.internal.ModbusManagerImpl] - Try 2 out of 3 failed when executing request (BasicModbusWriteCoilRequestBlueprint@89da23[slaveId=1,reference=0,functionCode=WRITE_COIL,bits=SingleBitArray(bit=1),maxTries=3]). Will try again soon. Error was: net.wimpi.modbus.ModbusSlaveException Error Code = 4 [operation ID c2ca648b-fe2c-44d5-a6c4-42099609d1cf]
16:10:25.096 [ERROR] [ort.modbus.internal.ModbusManagerImpl] - Last try 3 failed when executing request (BasicModbusWriteCoilRequestBlueprint@89da23[slaveId=1,reference=0,functionCode=WRITE_COIL,bits=SingleBitArray(bit=1),maxTries=3]). Aborting. Error was: net.wimpi.modbus.ModbusSlaveException Error Code = 4 [operation ID c2ca648b-fe2c-44d5-a6c4-42099609d1cf]
16:10:25.110 [ERROR] [ternal.handler.ModbusDataThingHandler] - Thing modbus:data:beckhoff:coils:do01 ‘Modbus Data’ had ModbusSlaveErrorResponseExceptionImpl error on write: ModbusSlaveErrorResponseException(error=4)
16:10:25.129 [INFO ] [ome.event.ThingStatusInfoChangedEvent] - ‘modbus:data:beckhoff:coils:do01’ changed from ONLINE to OFFLINE (COMMUNICATION_ERROR): Error (ModbusSlaveErrorResponseExceptionImpl) with write. Request: BasicModbusWriteCoilRequestBlueprint@89da23[slaveId=1,reference=0,functionCode=WRITE_COIL,bits=SingleBitArray(bit=1),maxTries=3]. Description: ModbusSlaveErrorResponseException(error=4). Message: Slave responsed with error=4
16:10:25.217 [INFO ] [ome.event.ThingStatusInfoChangedEvent] - ‘modbus:data:beckhoff:coils:do01’ changed from OFFLINE (COMMUNICATION_ERROR): Error (ModbusSlaveErrorResponseExceptionImpl) with write. Request: BasicModbusWriteCoilRequestBlueprint@89da23[slaveId=1,reference=0,functionCode=WRITE_COIL,bits=SingleBitArray(bit=1),maxTries=3]. Description: ModbusSlaveErrorResponseException(error=4). Message: Slave responsed with error=4 to ONLINE

Beckhoff
BC9100 (factory reseted and set to fieldbus)
4x KL1408 | 8-channel digital input
2x KL2408 | 8-channel digital output

RasberryPi

Things:
Bridge modbus:tcp:beckhoff [ host=“192.168.5.253”, port=502, id=1 ] {
Bridge poller discreteInputs [ start=0, length=32, refresh=1000, type=“discrete” ] {
Thing data di01 [ readStart=“0”, readValueType=“bit” ]
Thing data di02 [ readStart=“1”, readValueType=“bit” ]
}
Bridge poller coils [ start=0, length=16, refresh=1000, type=“coil” ] {
Thing data do01 [ readStart=“0”, readValueType=“bit”, writeStart=“0”, writeValueType=“bit”, writeType=“coil” ]
Thing data do02 [ readStart=“1”, readValueType=“bit”, writeStart=“1”, writeValueType=“bit”, writeType=“coil” ]
}
}

Items:
Switch DO01 “Digital Output index 01 [%d]” (beckhoff_out) { channel=“modbus:data:beckhoff:coils:do01:switch” }
Switch DO02 “Digital Output index 02 [%d]” (beckhoff_out) { channel=“modbus:data:beckhoff:coils:do02:switch” }

When changing output state from outside openhab the status changs in openhab without error msg

2020-04-07 16:28:02.952 [vent.ItemStateChangedEvent] - DO01 changed from ON to OFF
2020-04-07 16:28:07.413 [vent.ItemStateChangedEvent] - DO01 changed from OFF to ON

Anyone an idea please?

2

Modbus exception code 4 is a rejection from your PLC, “error”

It doesn’t like what your asking it to do.
I don’t know what your PLC might like instead; review the addressing of your coils, review if the PLC works with only one of FC05 or FC15 to write coils

3

No, but it does work, state is changing .. only getting the error msg on top .. so addressing should be ok (?)
tried with writetype holding and writeMultipleEvenWithSingleRegisterOrCoil
same or worse result

4

State gets updated because openHAB predicts it when the item receives a command.

You can disable this behavior using autoupdate flag in your item definition, see Modbus - Bindings | openHAB

With autoupdate disabled, I would expect the state to remain unchanged.

5

State does change on the KL2408 (led turns on/off) .. so it really works ..
(did already try with autoupdate set to false before)

1 Like
6

The exception code absolutely comes from your PLC.
If you think the expected write is working, i.e. accepted by the PLC, there remains the possibility that oipenHAB is issuing a “bad” write as well.

You’ve been tinkering with Thing settings in-flight, now reboot so that you know the binding is using only what you think are “good” settings.

1 Like
7

Did restart openhab few times and also reinstalled the modbus binding.
Restarted and reset beckhoff bc9000 too.
Still getting the error 4.

set log level to TRACE :
openHAB Add-ons :: Bundles :: Modbus Binding
openHAB Add-ons :: Bundles :: IO :: Modbus Transport
But extra info ..

8

This Beckhoff manual page describes why the PLC would respond with modbus exception code 4

the text is

Watchdog or K-bus error
EK9000: E-bus error

and they also make clear that illegal modbus commands would produce different EC to 4

On that basis, I’d say your openHAB config is fine, and the problem is with your PLC config.

It seems odd to both appear to “work” and report an error, but I suppose sometimes the PLC has to try to implement a command to discover an error, so there is a sort of sense there.

9

Checked and tried all terminals one by one (others removed)
Any Beckhoff/Modbus specialists around or ida how to further troubleshoot this?