Modbus Message Formats; Function 03 - Read Multiple Registers; Function 04 - Read Multiple Registers; Function 06 - Write Single Register - Satec PM172 Series Owner Reference Manual

3 MODBUS MESSAGE FORMATS

3.1 Function 03 - Read Multiple Registers

This command allows the user to obtain contents of up to 125 contiguous registers from a single data table.
Request
Instrument Function
Address (03)
1 byte 1 byte
Starting Address Address of the first register to be read
Word Count The number of contiguous words to be read
Response
Instrument Function
Address (03)
1 byte 1 byte
The byte count field contains quantity of bytes to be returned.

3.2 Function 04 - Read Multiple Registers

This command allows the user to obtain contents of up to 125 contiguous registers from a single data table. It can
be used instead of function 03.
Request
Instrument Function
Address (04)
1 byte 1 byte
Starting Address Address of the first register to be read
Word Count The number of contiguous words to be read
Response
Instrument Function
Address (04)
1 byte 1 byte
The byte count field contains quantity of bytes to be returned.

3.3 Function 06 - Write Single Register

This command allows the user to write the contents of a data register in any data table where a register can be
written.
Request
Instrument Function
Address (06)
1 byte 1 byte
Starting Address
Data Value
Response
The normal response is the retransmission of the write request.

3.4 Function 16 - Write Multiple Registers

This request allows the user to write the contents of multiple contiguous registers to a single data table where
registers can be written.
Starting
Address
2 bytes
Byte Data
Count Word 1
1 byte 2 bytes
Starting
Address
2 bytes
Byte Data
Count Word 1
1 byte 2 bytes
Starting
Address
2 bytes
Address of the register to be written
Data to be written to the register
Word Count Error Check
2 bytes 2 bytes
... Data Error
Word N Check
... 2 bytes 2 bytes
Word Count Error Check
2 bytes 2 bytes
... Data Error
Word N Check
... 2 bytes 2 bytes
Data Error check
Word
2 bytes 2 bytes
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