Schneider Electric Altivar 212 Principle of the Modbus protocol, RTU mode, Slave Slave j Slave k

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Modbus services

Principle of the Modbus protocol

The Modbus protocol is a master-slave protocol.

Only one device can transmit on the line at any one time.

The master manages the exchanges and only it can take the initiative.

It interrogates each of the slaves in succession.

No slave can send a message unless it is invited to do so.

Master

In the event of an error during data exchange, the master repeats the question and declares the interrogated slave absent if no response is received within a given time period.

If a slave does not understand a message, it sends an error response to the master. The master may or may not repeat the request.

Slave i

Slave j	Slave k

Two types of dialog are possible between master and slaves:

•The master sends a request to a slave and waits for it to respond. The request contains the slave address (1 ... 247).

•Broadcast: the master sends a request to all slaves. Slaves do not answer. The value of the slave address is 0.

Direct slave-to-slave communications are not possible.

For slave-to-slave communication, the master’s application software must therefore be designed to interrogate one slave and send back data received to the other slave.

RTU mode

ATV212 supports RTU mode.

The Modbus RTU frame contains no message header byte, nor end of message bytes.

It is defined as follows:

Slave address

Function code

Data

CRC16

The data is transmitted in binary code. CRC16: Cyclic redundancy check parameter.

The end of the frame is detected on a silence greater than or equal to 3 characters.

The master must not introduce a space of more than 3.5 characters in a frame; otherwise the drive may recognize it as a start of new frame.

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Contents Altivar S1A53844 01/2011 Table of Contents Table of Contents Safety Information Important InformationAbout the Book At a GlanceHazard of Electric SHOCK, Explosion or ARC Flash S1A53844 01/2011 Introduction Introduction Topic Hardware setupWhats in this Chapter? Pin out of the Open Style Modbus connector RJ45Cross section Tightening torqueConnection via Open Style wiring system Pin out of the RJ45 Modbus connectorPin Signal Open Style ReferenceConnection via RJ45 wiring system Connection accessoriesConnecting cables RJ45 ReferenceProtection Against Interference Description of terminals PTC resistor value F646GND Hardware setup Configuration Configuration of the communication parameters Access to the parametersParameters Modbus Adjustment range Default Valid Address AfterConfiguration of the control source Parameters Modbus SettingControl by the Modbus network CommunicationParameters Setting Default ValidControl by the terminals, monitoring by the Modbus network Parameters Modbus Setting Default Valid Parameters Modbus Setting Default Valid Address Com channel choice F807 Communication Menu COM submenuLI R selection F112 LI R selectionParameters Location Remote spd ref 2 F207Frequency source VIA VIAComplete control diagram Commands CMOdConfiguration of the indirect blocks ConfigurationConfiguration of the communication interruption Configure the drive behaviour Parameter Modbus Setting Default Valid AddressCommunication detected fault 16#851 2129Configuration Modbus services RTU mode Principle of the Modbus protocolSlave Slave j Slave k Slave address Function code DataFunction 3, quantity = Modbus functions availableRead one word Status info Read indirect blockFunction 3, quantity = 1 Read indirect block of 2 parameters Write Single Register Write multiple registers Function 16 = 16#10, quantity =1Speed Setpoint Command word Frequency SetpointWrite indirect block Request 6C 7E Response Read Device Identification 43/14 Error response Exception codeModbus services Parameter list Auto ramp AUI Disabled Manual Setting of Max frequency FHReferring to the Altivar 212 programming manual GeneralCommands from serial communication List of control parametersSetpoints from serial communication Outputs control from serial communicationList of monitoring parameters StatusFrequency and speed Current and torquePower and energy MaintenanceTrip and alarm codes ValuesBit Specifications Remarks CommandsCommand word FA00 Command word 2 FA20 Energy reset bitExamples Over-current stall level change bitSpeed setpoint FA13 SetpointsFrequency setpoint FA01 Status Status word FE0I Fd01Command mode status FE45 Setpoint mode status FE46Status word 2 FE42 Fd42 Status word 3 FE49 Fd49Alarm of run time FE79 Trip and alarm codesAlarm code FC91 Code Value Description Hexadecimal number Decimal number Monitoring and control of I/O from communication Digital inputs status Fd06, FE06Digital outputs status Fd07, FE07 Bit Terminal name Function parameter titleDigital outputs command FA50 Analog outputs command FA51Damper opening command Analog inputs values FE35, FE36F580 = 3 Drive model code F805 Model Voltage Power Rating Code FB05 Class FB72bit8Identification ATV212WU15N4C S1A53844 01/2011 Appendix RS485 standard Modbus 2-wire standard schematicSchematic diagram Migration Commissioning Migration ATV21 ATV212For example ATV212Modbus manualENS1A5384401 S1A53844 01/2011