User Guide - Eurotherm Ltda

nanodac RECORDER/CONTROLLER: USER GUIDE5.2.1 Function Codes (Cont.)EXCEPTION CODESMODBUS TCP provides reserved codes used for exceptions. These codes provide error information relatingto failed requests. Exceptions are signalled by hex 80 being added to the function code of the request,followed by one of the codes listed in table 8.2.1b, below.CodeDec Hex01 01Modbus definitionIllegal functionDescription (see Modbus specification for full details)An invalid function code was received0202Illegal Data AddressAn invalid data address was received0303Illegal Data ValueAn invalid data value was received0404Slave Device FailureAn unrecoverable error occurred in the instrument0909Illegal Sub FunctionAn invalid sub function was received100AGateway path unavailableGateway misconfigured or overloaded110BGateway target device failedto respondDevice not present on the networkTable 5.2.1b Exception codes5.2.2 Data typesThe following data types are supported:1. 2's complement signed 16-bit analogue values with implied decimal point. The decimal point positionmust be configured in both the recorder and the host computer.2. 16, 32 and 64 bit signed integers.3. 16-bit unsigned integer values.4. 32 bit IEEE Floating point values.5. Strings of limited size, can be transferred across Modbus TCP in Unicode format using a single nonmultiplexedset of consecutive registers.DATA ENCODINGMODBUS uses what is called a 'Big endian' representation for addresses and data items. This means thatwhen a numerical quantity larger than a single byte is transmitted, the most significant byte is sent first. Forexample a 32-bit hex value of 12345678 would be transmitted as 12, followed by 34, followed by 56 andfinally 78.5.2.3 Invalid multiple register writesWhen a recorder receives a multi-register write request, it is possible that one or more requests will be rejected.Under such a circumstance, the recorder accepts all valid write requests and ignores any invalidwrites. No error response is produced.5.2.4 Master communications timeoutWhilst the instrument is archiving, it is possible that communications responses slow sufficiently to causecommunications timouts. The Modbus master device should be configured with a timout value largeenough to ensure against nuisance timeouts during archiving.HA030554Issue 7 Nov 12Page 171