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CHAPTER 3: MODBUS FUNCTIONS FUNCTION CODE 05H: EXECUTE OPERATION

750/760 FEEDER MANAGEMENT RELAY – COMMUNICATIONS GUIDE 3 - 3

Since some PLC implementations of Modbus only support one of function codes 03h and

04h, the 750/760 interpretation allows either function code to be used for reading one or

more consecutive data registers. The data starting address will determine the type of data

being read. Function Codes 03h and 04h are therefore identical.

The following table shows the format of the master and slave packets. The example shows

a master device requesting 3 register values starting at address 200h from slave device 11;

the slave device responds with the values 555, 0, and 100 from registers 200h, 201h, and

202h respectively.

Function Code 05h: Execute Operation

This function code allows the master to perform various operations in the 750/760.

Operations are shown in the Summary of Operation Codes for Function 05h table.

The following table shows the format of the master and slave packets. The example shows

a master device requesting the slave device 11 to perform a reset. The ‘high’ and ‘low’

Code Value bytes always have the values FFh and 00h, respectively and are a remnant of

the original Modbus definition of this function code.

Master Transmission Bytes Example Description

Slave Address 1 11 message for slave 11

Function Code 1 03 read register values

Data Starting Address 2 02 00 data starting at 0200h

Number of Registers 2 00 03 3 registers = 6 bytes total

CRC (low, high) 2 06 E3 computed CRC error code

Slave Response Bytes Example Description

Slave Address 1 11 message from slave 11

Function Code 1 03 read register values

Byte Count 1 06 3 values = 6 bytes total

Data #1 (high, low) 2 02 2B value in address 0200h

Data #2 (high, low) 2 00 00 value in address 0201h

Data #3 (high, low) 2 00 64 value in address 0202h

CRC (low, high) 2 C8 BA computed CRC error code

Master Transmission Bytes Example Description

Slave Address 1 11 message for slave 11

Function Code 1 05 execute operation

Operation Code 2 00 01 remote reset

Code Value 2 FF 00 perform operation

CRC (low, high) 2 DF 6A computed CRC error code

Slave Response Bytes Example Description

Slave Address 1 11 message from slave 11

Function Code 1 05 execute operation

GE 750 Guide

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