Circutor computer SMART III-Fast Series Manuale Utente Scaricare il pdf (Pagina 59)

4�9�2� PROTOCOL

TheModbusprotocolisanindustrycommunicationstandardwhichenablesnetworkingof

multipleunits,withonemasterandseveralslaves�Itallowsindividualmaster-slavedialogue

andalsoenablescommandsinbroadcastformat�

IntheModbusprotocol,theComputer SMART III FASTunitusestheRTU(RemoteTerminal

Unit)mode�

IntheRTUmode,themessagestartandendaredetectedwithsilencesofatleast3�5

characters,andthe16-bitCRCerror-detectionmethodisused�

TheModbus functionsimplementedintheunitareasfollows:

Function 01�Readingthestatusoftherelays�

Functions 03 and 04�Readinglogs�

Function 05�Writingarelay�

Function 0F�Writingmultiplerelays�

Function 10�Writingmultiplelogs�

Exception codes

Ifthebitwithgreatestweightofthebytecorrespondingtothefunctioninthereplyoftheunit

is1,thisindicatesthatthenextbyteisanexceptioncode�

Table 11: Exception codes, Modbus communications�

Exception code Description

01 Incorrectfunction�Thefunctionnumberisnotimplemented�

02 Incorrectaddressornumberoflogsoutoflimits

03 Dataerror�ACRCerrorhasoccurred

04 Peripheralerror�Anerroroccurredwhenaccessingaperipheral(EE-

PROM,card,etc�)

06 SlaveerrororSlavebusy�Retrysending�

Example:

Address Function

Exception

code

CRC

0A 84 01 XXXX

Address: 0A,Peripheralnumber:10indecimal�

Function: 84,Readingfunction04withbitno�7at1�

Exception code: 01,seeTable 9�

CRC:16-bitCRC�

Forreasonsofoperationalsecurityoftheunit,communicationframesof

morethan80bytesarenotaccepted(sentorreceived)�

Instruction Manual

Computer SMART III FAST

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Circutor computer SMART III-Fast Series Manuale Utente Pagina 59