MA Relay Modbus User Manual 02A
Contents
1. Is an error response called an exception response and the data bytes will contain a code that describes the error The exception response is identified by the function code being a copy of the query function code but with the most significant bit set to logic 1 Slave Address 5 bit value representing the address of slave which has Just responded Function Code 5 bit value which ls the function code in the query OR ed with Hex 50 indicating the slave either does not recognise the query or could not car the action requested Error Code 8 bit value indicating the nature of the exception detected See Exception Codes in the section Product Information for a list of SPR and Integra supported codes Error Check Lo The bottom check value Y out as east significant eight bits of a 16 bit number representing the error he top most significant eight bits of a 16 bit number representing the error check value Using the ModbusModSetup Tool to change Modbus address and BAUD rate 2 ModbusMod NewElec Pretoria Pty Sala File CONNECT Unit Address Comm Port 10 ag Bus Baud Rate 1200bps Read v ribe Open the ModbusModSetup exe application in the Information Downloads MA Relay Downloads Doc Modbus Docs ModBusMod Interface directory on the NewElec Application install CD When the application is opened select the correct communication po2. bit number specifying the number of registers being requested Error Check Lo The bottom least significant eight bits of a 16 bit number representing the error check value Error Check Hi The top most significant eight bits of a 16 bit number representing the error check value Response The example illustrates the normal response to a request for a single 15 bit Register Function yte Data Hi Code Slave Address 68 bit value representing the address of slave which has just responded Function Code 6 bit value which when a copy of the function code in the query indicates that the slave recognised the query and has responded See also Exception Response Byte Count 86 bit value indicating the number of data bytes contained within this response Data Hi The top most significant eight bits of a 16 bit number representing the register s requested in the query The bottom least significant elght bits of a 16 bit number representing the register s requested in the query Data Lo Error Check Lo The bottom least significant eight bits of a 16 bit number representing the error check value Error Check Hi The top most significant eight bits of a 16 bit number representing the error check value Exception Response lf an error is detected in the content of the query excluding parity errors and Error Check mismatch the function code will be modified to indicate that the response
3. dures for aKa Mel aad a a e ing up proce aay Ver 2 0 d sett Modbus Module 10N an MA MOTOR PROTECTION amp Installat CONTROL RELAY 26 June 2008 ESSE a oo aaa a SSS SEES EEEE o es o a Ds a a a o as a ds a o ES aa j o o Picture Layout of MA Relay with Modbus Module ae 7 7 AN 7 Description of Modbus Module Connections I2C Port Used as an engineering port to change the modules Modbus Address and baud rate Pin assignment 1 VDD 2 3 CL 3 SDA 4 Rx Sn Tx 6 GND This port can also be used with expansion modules e g FLED unit 5 Pin Modbus RTU connection GND Ground connection Optional A Modbus High connection SCRN Cable Screen connection Optional B Modbus Low Connection 5V Output voltage of 5 Volt No connection required for Modbus DB9 Modbus RTU connection 1 SCRN N C Modbus Connection A N C GND 5V N C Modbus Connection B N C te E What is RS485 RS465 or EIA Electronic Industries Association R5455 is a balanced line half duplex transmission system allowing transmission distances of up to 1 2 km The following table summarises the RS 485 Standard PARAMETER Mode of Operation Differential Number of Drivers and Receivers 32 Drivers 32 Receivers Maximum cable length metres Maximum data rate baud Maximum common mode voltage Volts Minimum Driver Output Leve
4. ls Loaded 15 Minimum Driver Output Levels G Unloaded Drive Load Ohms 60 min Driver Output short circuit current Limit 150 to Gnd 250 to 7 or 12 W mA Minimum receiver input Resistance konms Receiver sensitivity 200mv What is half duplex Halt duplex Is a system in which one or more transmitters talkers can communicate with one or more receivers listeners with only one transmitter being active at any one time For example a conversation is Started by asking a question the person who has asked the question will then listen until he gets an answer or until he decides that the individual who was asked the question is not going to reply In a 485 network the master will start the conversation with a Query addressed to a specific slave the master will then listen for the slave s response If the slave does not respond within a pre defined period set by control software in the master the master will abandon the conversation Connecting the Instruments Screened twisted pair cable should be used All A connections should be connected together using one conductor of the twisted pair cable all B connections should be connected together using the other conductor in the pair The cable screen should be connected to the Gnd terminal A Belden 9841 Single pair or 9842 Two pair cable with a characteristic impedance
5. of 120 ohms is recommended the cable should be terminated at each end with a 120 ohm quarter watt or greater resistor There must be no more than two wires connected to each terminal this ensures that a Daisy Chain or straight line configuration is used A Star or a network with Stubs Tees is not recommended as reflections within the cable may result in data corruption Dalsy Chained Connection Correct Which is A and Which is B The A and B connections to the SPR and Integra Products can be identified by the signals present on them whilst there is activity on the RS485 bus Start Bit Idle State i Idle State B MODBUS Messages Communication on a MODBUS Network is initiated started by a Master with a query to a Slave The Slave which is constantly monitoring the network for Queries will recognise only the Queries addressed to it and will respond either by performing an action setting a value for example or by returning a response Only the Master can initiate a query Slave 1 Slave 2 Slave 3 Slave n i TiL Le y In the MODBUS protocol the master can address individual slaves or using a special Broadcast address can initiate a broadcast message to all slaves The SPR and Integra products do not support the broadcast address MODBUS Message Format The MODBUS protocol defines the format for the master s query and the slave
6. rt you have connected to the Modbus slave Comm Port i COM C COM2 C COM3 with a CAB0004 cable and a CAB0013 adaptor cable connected and plugged into the I2C Port Then Click on Connect on the menu bar 2 ModbusMod NewElec Fie CONNECT Umt Address L Enter the required slave address J Unit Address Select the required baud rate 2 ModbusMod NewElec Pretoria Pty Elx File CONNECT Unit Address Comm Port E COM C come Bus Baud Hate 12U00bps hal C COMa 1200bps 2400bps 4600 bps abOObps 1200bps 30400bp And click on the Write button to update the slave To read up the configuration from the slave just click on the Read button
7. s response The query contains the device or broadcast address a function code defining the requested action any data to be sent and an error checkinag field The response contains fields confirming the action taken any data to be returned and an error checking field If an error occurred in receipt of the message or If the slave Is unable to perform the requested action the slave will construct an error message and send It as its response Query The example illustrates a request for a single 16 bit Modbus Register Start Number Number rror Error Address Address of Points of Points Chec Check Hi Lo Hi 1 Hi Slave Address amp bit value representing the slave being addressed 1 to 247 0 ls reserved for the broadcast address The SPR and Integra products do not support the broadcast address Function Code 6 bit value telling the addressed slave what action is to be performed 3 4 or 16 are valid for integra Start Address Hi The top most significant eight bits of a 16 bit number specifying the start address of the data being requested Start Address Lo The bottom least significant eight bits of a 16 bit number specifying the start address of the data being requested Number of Points Hi The top most significant eight bits of a 16 bit number specifying the number of registers being requested Number of Points Lo The bottom least significant eight bits of a 16
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