ModbusPlustoEthernetBridge
5
Table 2 SummaryofModbusDataAccessCommands
FunctionCode(Decimal)Command Name
1ReadDiscreteOutputStatus(0xxxx)
2ReadDiscreteInputStatus(1xxxx)
3ReadOutputRegister (4xxxx)
4ReadInputRegister (3xxxx)
5ForceSingleCoil(0xxxx)
6PresetSingleRegister(4xxxx)
7ReadException Status
8Subfunction21 Get/ClearNetworkStatistics
15 ForceMultipleCoils(0xxxx)
16 PresetMultipleRegisters(4xxxx)
17 ReportSlaveID
Deviceswhich usethe Modbusprotocolacceptincoming requestsfordata or
statistics.Theyreplybyreturning eithera normaloran exception response.
TheModbusfunction code inthe request froman originating node always contains
amostsignificantbitvalueof0(zero). In anormalModbusresponse, the function
code of the originating requestisechoed, followed byanyrequested data or
statistics. In an exception response, the mostsignificantbitis set to1(one)to
indicate an error,andthe nextbytecontainsan exception code showing the
reason forthe error.
Table 3 summarizesthe Modbusexception codeswhichmaybe returned bythe
bridge tothe originating node.Forfurtherinformation see the ModbusProtocol
ReferenceGuide,publication PI--MBUS--300.
Table 3 SummaryofModbusExceptionCodes
ExceptionCode(Hexadecimal)Meaning
01 Illegalfunction
02 Illegaldataaddress
03 Illegaldatavalue
04 Unexpectedfailure during command execution
05 ACK----Requested operation isin progress
06 BUSY ----Notreadyto performrequested operation
07 NAK ----Requested operation rejected
08 Couldnotopen ModbusPluspath
09 ErrorduringModbusPlus send
0A ErrorduringModbusPlusreply