So, I set one holding register in OPC and I see this traffic:
(COM4) Tx: [0008] 02 03 00 01 00 01 D5 F9
(COM4) Rx: [0007] 02 03 02 05 87 BF 76
and after it I stoped OPC and closed this programm. After it I started OH and I saw this log
2019-06-17 21:28:04.403 [ERROR] [t.wimpi.modbus.io.ModbusRTUTransport] - Last request: 02 03 00 01 00 01 d5 f9
2019-06-17 21:28:04.403 [ERROR] [t.wimpi.modbus.io.ModbusRTUTransport] - failed to read: Error reading response (EOF)
2019-06-17 21:28:04.404 [ERROR] [pi.modbus.io.ModbusSerialTransaction] - execute try 1/1 error: I/O exception: IOException Error reading response (EOF). Request: net.wimpi.modbus.msg.ReadMultipleRegistersRequest@806b0e5 (unit id 2 & transaction 130). Serial parameters: SerialParameters@22725c39[portName=COM4,baudRate=115200,flowControlIn=none,flowControlOut=none,databits=8,stopbits=1,parity=none,encoding=rtu,echo=false,receiveTimeoutMillis=1500]
2019-06-17 21:28:04.404 [ERROR] [pi.modbus.io.ModbusSerialTransaction] - execute reached max tries 1, throwing last error: I/O exception: IOException Error reading response (EOF). Request: net.wimpi.modbus.msg.ReadMultipleRegistersRequest@806b0e5 (unit id 2 & transaction 130). Serial parameters: SerialParameters@22725c39[portName=COM4,baudRate=115200,flowControlIn=none,flowControlOut=none,databits=8,stopbits=1,parity=none,encoding=rtu,echo=false,receiveTimeoutMillis=1500]
2019-06-17 21:28:04.404 [WARN ] [rt.modbus.internal.ModbusManagerImpl] - Try 1 out of 3 failed when executing request (ModbusPollerThingHandlerImpl.ModbusPollerReadRequest@2cfaf8d5[slaveId=2,functionCode=READ_MULTIPLE_REGISTERS,start=1,length=1,maxTries=3]). Will try again soon. Error was I/O error, so reseting the connection. Error details: net.wimpi.modbus.ModbusIOException I/O exception: IOException Error reading response (EOF) [operation ID 25172098-85b3-489c-bd4c-2b95873afa87]
2019-06-17 21:28:05.950 [ERROR] [t.wimpi.modbus.io.ModbusRTUTransport] - Last request: 02 03 00 01 00 01 d5 f9
2019-06-17 21:28:05.951 [ERROR] [t.wimpi.modbus.io.ModbusRTUTransport] - failed to read: Error reading response (EOF)
2019-06-17 21:28:05.951 [ERROR] [pi.modbus.io.ModbusSerialTransaction] - execute try 1/1 error: I/O exception: IOException Error reading response (EOF). Request: net.wimpi.modbus.msg.ReadMultipleRegistersRequest@23566edb (unit id 2 & transaction 131). Serial parameters: SerialParameters@22725c39[portName=COM4,baudRate=115200,flowControlIn=none,flowControlOut=none,databits=8,stopbits=1,parity=none,encoding=rtu,echo=false,receiveTimeoutMillis=1500]
2019-06-17 21:28:05.952 [ERROR] [pi.modbus.io.ModbusSerialTransaction] - execute reached max tries 1, throwing last error: I/O exception: IOException Error reading response (EOF). Request: net.wimpi.modbus.msg.ReadMultipleRegistersRequest@23566edb (unit id 2 & transaction 131). Serial parameters: SerialParameters@22725c39[portName=COM4,baudRate=115200,flowControlIn=none,flowControlOut=none,databits=8,stopbits=1,parity=none,encoding=rtu,echo=false,receiveTimeoutMillis=1500]
2019-06-17 21:28:05.952 [WARN ] [rt.modbus.internal.ModbusManagerImpl] - Try 2 out of 3 failed when executing request (ModbusPollerThingHandlerImpl.ModbusPollerReadRequest@2cfaf8d5[slaveId=2,functionCode=READ_MULTIPLE_REGISTERS,start=1,length=1,maxTries=3]). Will try again soon. Error was I/O error, so reseting the connection. Error details: net.wimpi.modbus.ModbusIOException I/O exception: IOException Error reading response (EOF) [operation ID 25172098-85b3-489c-bd4c-2b95873afa87]
2019-06-17 21:28:07.497 [ERROR] [t.wimpi.modbus.io.ModbusRTUTransport] - Last request: 02 03 00 01 00 01 d5 f9
2019-06-17 21:28:07.497 [ERROR] [t.wimpi.modbus.io.ModbusRTUTransport] - failed to read: Error reading response (EOF)
2019-06-17 21:28:07.498 [ERROR] [pi.modbus.io.ModbusSerialTransaction] - execute try 1/1 error: I/O exception: IOException Error reading response (EOF). Request: net.wimpi.modbus.msg.ReadMultipleRegistersRequest@5250b5b8 (unit id 2 & transaction 132). Serial parameters: SerialParameters@22725c39[portName=COM4,baudRate=115200,flowControlIn=none,flowControlOut=none,databits=8,stopbits=1,parity=none,encoding=rtu,echo=false,receiveTimeoutMillis=1500]
2019-06-17 21:28:07.498 [ERROR] [pi.modbus.io.ModbusSerialTransaction] - execute reached max tries 1, throwing last error: I/O exception: IOException Error reading response (EOF). Request: net.wimpi.modbus.msg.ReadMultipleRegistersRequest@5250b5b8 (unit id 2 & transaction 132). Serial parameters: SerialParameters@22725c39[portName=COM4,baudRate=115200,flowControlIn=none,flowControlOut=none,databits=8,stopbits=1,parity=none,encoding=rtu,echo=false,receiveTimeoutMillis=1500]
2019-06-17 21:28:07.498 [ERROR] [rt.modbus.internal.ModbusManagerImpl] - Last try 3 failed when executing request (ModbusPollerThingHandlerImpl.ModbusPollerReadRequest@2cfaf8d5[slaveId=2,functionCode=READ_MULTIPLE_REGISTERS,start=1,length=1,maxTries=3]). Aborting. Error was I/O error, so reseting the connection. Error details: net.wimpi.modbus.ModbusIOException I/O exception: IOException Error reading response (EOF) [operation ID 25172098-85b3-489c-bd4c-2b95873afa87]
2019-06-17 21:28:07.501 [ERROR] [ernal.handler.ModbusDataThingHandler] - Thing modbus:data:c93c902e ‘Modbus data_ARD1’ had ModbusSlaveIOExceptionImpl error on read: ModbusSlaveIOException(cause=ModbusIOException, EOF=false, message=‘I/O exception: IOException Error reading response (EOF)’, cause2=null)