Chapter 7 Modbus Communications
7-1 Functions Supported
Only function 03, 06 and 16 are available for this series of controllers. The message formats for each function are
described as follows:
Query (from master)
Response (from slave)
Slave address (0-255)
Function code (3)
Starting address of register Hi (0)
Starting address of register Lo (0-79)
No. of words Hi (0)
No. of words Lo (1-79)
CRC16 Hi
CRC16 Lo
Byte count
Data 1 Hi
Data 1 Lo
Data 2 Hi
Data 2 Lo
CRC16 Hi
CRC16 Lo
Function 03: Read Holding Registers
Function 06: Preset single Register
Query (from master)
Response (from slave)
Slave address (0-255)
Function code (6)
Register address Hi (0)
Register address Lo (0-79, 128-131)
Data Hi
Data Lo
CRC16 Hi
CRC16 Lo
Query (from master)
Response (from slave)
Slave address (0-255)
Function code (16)
Starting address of register Hi (0)
Starting address of register Lo (0-79, 128-131)
No. of words Hi (0)
No. of words Lo (1-79)
Byte count (2-158)
Data 1 Hi
Data 1 Lo
Data 2 Hi
Data 2 Lo
CRC16 Hi
CRC16 Lo
CRC16 Hi
CRC16 Lo
Function 16: Preset Multiple Registers
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