User Documentation

Communications
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9.4 MODBUS (RTU) communication
9.4.1 Overview of MODBUS (RTU)
8-bit binary data in command is transmitted as it is.
Data format Start bit 1 bit
Data bit 8 bits (fixed)
Parity No parity, even parity, odd parity selectable
Stop bit 1-bit, 2-bit selectable
Error detection CRC-16 (Cyclic Redundancy Check)
Data interval 3.5 character transmission time or less
Message configuration
RTU mode is configured to start after idle time processing of more than 3.5 character transmissions and end
after idle time processing of more than 3.5 character transmissions.
3.5 idle
characters
Slave
address
Function
code
Data
Error check
CRC-16
3.5 idle
characters
8-bit 8-bit xx bits 16-bit
Master judges the transmission complete after no command for 4-characters idle time and processes the
command.
Transmission speed and judgment time to complete transmission
Transmission speed (bps) Judgment time to complete (ms)
38400 about 1
19200 about 2
9600 about 4
4800 about 8
2400 about 16
1200 about 32