Chapter 9 Modbus Communications - Brainchild BTC-2500 User Manual

Chapter 9 Modbus Communications

Chapter 9 Modbus Communications
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 300, 600, 1200, 2400, 4800, 9600, 14400, 19200, 28800 and
38400.
9 1 Functions Supported 9 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:
Function 03: Read Holding Registers Function 03: Read Holding Registers
Query Query ( from master )
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
Function 06: Preset single Register Function 06: Preset single Register
Query Query ( from master )
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 Function 16: Preset Multiple Registers
Query Query ( from master )
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
110
Response ( from slave ) Response
Byte count
Data 1 Hi
Data 1 Lo
128-131)
Data 2 Hi
Data 2 Lo
CRC16 Hi
CRC16 Lo
Response ( from slave ) Response
Response Response ( from slave )
CRC16 Hi
CRC16 Lo
UM25001H