Brainchild P91 - Chapter 7 Modbus Communications; 7-1 Functions Supported

Chapter 7 Modbus CommunicationsChapter 7 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 2400, 4800, 9600, 14400, 19200, 28800 and 38400.
7-1 Functions Supported7-1 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 )
Query
Response ( from slave )Response
Slave address (1-247)
Function code (3)
Starting address of register Hi (0)
Starting address of register Lo (0-117,
128-143)
No. of words Hi (0)
No. of words Lo (1-118)
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 RegistersFunction 03: Read Holding Registers
Function 06: Preset single RegisterFunction 06: Preset single Register
Query ( from master )Query
Response ( from slave )Response
Slave address (1-247)
Function code (6)
Register address Hi (0)
Register address Lo (0-117, 128-143)
Data Hi
Data Lo
CRC16 Hi
CRC16 Lo
UM0P411A
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