Schweitzer Engineering Laboratories SEL-701, Instruction Manual

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701 Motor Protection Relay
Date Code 20010719
Modbus
®
RTU Communications Protocol
04h Read Input Registers Command
C.8
04h Read Input Registers Command
Use function code 04h to read from the Modbus map shown in Table C.18 on
page C.19 . You may read a maximum of 125 registers at once with this function code.
Table C.7 04h Read Input Registers Command
Table C.7 04h Read Input Registers Command
Bytes Field
The Master Request Must Have the Following Format
1 byte Slave address
1 byte Function code (04h)
2 bytes Starting register address
2 bytes Number of registers to read
2 bytes CRC-16 for message
A Successful SEL-701 Relay Response Will Have the Following Format
1 byte Slave address
1 byte Function code (04h)
1 byte Byte count (should be twice number of registers read)
n bytes Byte count bytes of data
2 bytes CRC-16 for message