Schweitzer Engineering Laboratories SEL-734 - Table F.9 03 H Read Holding Register Command; Table F.10 Responses to 03 H Read Holding Register Query Errors

F.5
Date Code 20090730 Instruction Manual SEL-734 Meter
Modbus RTU Communications Protocol
Modbus RTU Communications Protocol
03h Read Holding
Register Command
Use function code 03h to read directly from the Modbus Register Map shown
in Table F.23.
You can read a maximum of 125 registers at once with this function code.
Most masters use 4X references with this function code. If you are
accustomed to 4X references with this function code, for five-digit addressing,
add 40001 to the standard database address.
The meter responses to errors in the query are shown in Table F.1 0.
04h Read Input
Registers Command
Use function code 04h to read from the Modbus Register Map shown in
Table F.23.
You can read a maximum of 125 registers at once with this function code.
Most masters use 3X references with this function code. If you are
accustomed to 3X references with this function code, for five-digit addressing,
add 30001 to the standard database address.
Table F.9 03h Read Holding Register Command
Bytes Field
Requests from the master must have the following format:
1 byte Slave Address
1 byte Function Code (03h)
2 bytes Starting Register Address
2 bytes Number of Registers to Read
2 bytes CRC-16
A successful response from the slave will have the following format:
1 byte Slave Address
1 byte Function Code (03h)
1 byte Bytes of data (n)
n bytes Data
2 bytes CRC-16
Table F.10 Responses to 03h Read Holding Register Query Errors
Error Error Code Returned
Communication Counter
Increments
Illegal register to read Illegal Data Address (02h) Invalid Address
Illegal number of
registers to read
Illegal Data Value (03h) Illegal Register
Format error Illegal Data Value (03h) Bad Packet Format
Busy Slave is busy with other
task (06h)
Courtesy of NationalSwitchgear.com