Instruction manual

25
Chapter 7 Modbus Communications
Function 03: Read Holding Registers
Query: (from Master) Response: (from Slave)
Slave address (0-255)
Function code (3)
Starting address of register Hi (0) Byte count
Starting address of register Lo Data 1 Hi
(0-79, 128-131) Data 1 Lo
No. of words Hi (0) Data 2 Hi
No. of words Lo (1-79) Data 2 Lo
CRC16 Hi •
CRC16 Lo •
•
•
•
CRC16 Hi
CRC16 Lo
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
Function 16: Preset Multiple Registers
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) CRC16 Hi
Data 1 Hi CRC16 Lo
Data 1 Lo
Data 2 Hi
Data 2 Lo
•
•
•
•
•
CRC16 Hi
CRC16 Lo
This chapter specifies the Modbus Communications protocol as
RS-232 or RS-485 interface module is installed. Only RTU mode is supported. Data is transmitted
as eight-bit binary bytes with 1 start bit, 1 stop bit and optional parity checking (None, Even or
Odd). Baud rate may be set to 2400, 4800, 9600, 14400, 19200, 28800 and 38400.
7-1 Functions Supported
O
nly function 03, 06 and 16 are available for this series of controllers. The message formats for
each function are described as follows: