Technical data

Function Code 6 – Write Single Register
Send Format:
• :, ADDR, FC, START_REG MSB, START_REG LSB, DATA MSB, DATA LSB, LRC, CR, LF
Response Format:
• :,ADDR, FC, START_REG MSB, START_REG LSB, DATA MSB, DATA LSB, LRC, CR, LF
Function Code 16 – Write Multiple Registers
Send Format:
• :, ADDR, FC, START_REG MSB, START_REG LSB, REG_CNT MSB, REG_CNT LSB,
BYTE_CNT, ...DATA..., LRC, CR, LF
Response Format:
• :, ADDR, FC, START_REG MSB, START_REG LSB, REG_CNT MSB, REG_CNT LSB, LRC,
CR, LF
D.1.2 RTU Modbus Format
RTU Modbus uses the timing between character transmission to frame a message. The
receiving device monitors the elapsed time between receipt of characters. If three and
one-half character times elapse without receipt of a new character, then the received
message is completed. Thus, the time between transmitting characters within a message
must not be longer than three and one-half character times otherwise the receiving device
will prematurely declare the message complete. The communication parameters for RTU
Modbus are 8 data bits, no parity, and one stop bit.
The RTU Modbus formats for the supported Modbus functions are described below.
Function Code 3 – Read Multiple Registers
Send Format:
• TFRAME, ADDR, FC, START_REG MSB, START_REG LSB, REG_CNT MSB, REG_CNT
LSB, CRC_LOW, CRC_HI, TFRAME
Response Format:
• TFRAME, ADDR, FC, BYTE_CNT, ...DATA..., CRC_LOW, CRC_HI, TFRAME
Function Code 6 – Write Single Register
Send Format:
• TFRAME, ADDR, FC, START_REG MSB, START_REG LSB, DATA MSB, DATA LSB,
CRC_LOW, CRC_HI, TFRAME
Response Format:
• TFRAME, ADDR, FC, START_REG MSB, START_REG LSB, DATA MSB, DATA LSB,
CRC_LOW, CRC_HI, TFRAME
Modbus communications
Operations 123