Hi community,
I am new to modbus so the problem i deal with is possibly not that hard. Just an fundamental misunderstanding on how modbus works 
I am running openhab 2.4 beta version on Ubuntu with the newest Modbus binding to be released in the next update.
I am trying to read some temperature readings out of my central floor heating system - Wavin AHC9000
But i keep getting errors
I have some documentation on the system here
Wavin’s Modbus Specification
First of all i am trying to read the green line from this address sheet
My things file looks like this
Bridge modbus:serial:wavin [ port="/dev/ttyUSB0", baud=38400, stopBits="1.0", parity="none", dataBits=8, encoding="rtu" ] {
Bridge poller input [ start=16403, length=1, refresh=600, type="input" ] {
Thing data ARC1 [ readStart="16403", readValueType="uint16" ]
}
}
And my items file…
Number warc1 "[%f]" {channel="modbus:data:wavin:input:ARC1:number"}
And the sitemap
Frame label="Test" {
Default item=warc1 label="Bad Stue [%.1f °C]"
}
And lastly the log file
2018-10-03 19:15:58.106 [TRACE] [et.wimpi.modbus.net.SerialConnection] - Got Port Identifier
2018-10-03 19:15:58.120 [TRACE] [et.wimpi.modbus.net.SerialConnection] - Got Serial Port
2018-10-03 19:15:58.123 [TRACE] [et.wimpi.modbus.net.SerialConnection] - i/o Streams prepared
2018-10-03 19:15:58.128 [DEBUG] [t.wimpi.modbus.io.ModbusRTUTransport] - Sent: 01 04 40 13 00 01 d5 cf
2018-10-03 19:15:58.145 [TRACE] [t.wimpi.modbus.io.ModbusRTUTransport] - Managed to read at least one byte
2018-10-03 19:15:58.146 [DEBUG] [t.wimpi.modbus.io.ModbusRTUTransport] - Response: 01 84
2018-10-03 19:15:58.146 [ERROR] [t.wimpi.modbus.io.ModbusRTUTransport] - Last request: 01 04 40 13 00 01 d5 cf
2018-10-03 19:15:58.147 [ERROR] [t.wimpi.modbus.io.ModbusRTUTransport] - failed to read: CRC Error in received frame: 0 bytes:
2018-10-03 19:15:58.148 [ERROR] [pi.modbus.io.ModbusSerialTransaction] - execute try 1/1 error: I/O exception: IOException CRC Error in received frame: 0 bytes: . Request: net.wimpi.modbus.msg.ReadInputRegistersRequest@f8e055 (unit id 1 & transaction 605). Serial parameters: SerialParameters@1e85831[portName=/dev/ttyUSB0,baudRate=38400,flowControlIn=none,flowControlOut=none,databits=8,stopbits=1,parity=none,encoding=rtu,echo=false,receiveTimeoutMillis=1500]
2018-10-03 19:15:58.149 [ERROR] [pi.modbus.io.ModbusSerialTransaction] - execute reached max tries 1, throwing last error: I/O exception: IOException CRC Error in received frame: 0 bytes: . Request: net.wimpi.modbus.msg.ReadInputRegistersRequest@f8e055 (unit id 1 & transaction 605). Serial parameters: SerialParameters@1e85831[portName=/dev/ttyUSB0,baudRate=38400,flowControlIn=none,flowControlOut=none,databits=8,stopbits=1,parity=none,encoding=rtu,echo=false,receiveTimeoutMillis=1500]
2018-10-03 19:15:58.149 [WARN ] [rt.modbus.internal.ModbusManagerImpl] - Try 2 out of 3 failed when executing request (ModbusPollerThingHandlerImpl.ModbusPollerReadRequest@1d612bb[slaveId=1,functionCode=READ_INPUT_REGISTERS,start=16403,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 CRC Error in received frame: 0 bytes: [operation ID 77ed1fec-a994-4a06-9460-6d7a5d60ddd6]
I hope any of you can spread some light on how i get this working 
Best regards
Henrik Petersen