7-83
MODBUS RTU command message frame
START ADDRESS FUNCTION DATA CRC CHECK END
3.5-character time 8 bits 8 bits n*8 bits 16 bits 3.5-character time
ADDRESS (Unit No.) 8 bits, 0 to 99 (decimal)
Note1) 0= Broadcast address
Note2) Slave unit No. is 1 to 99 (decimal)
Note3) For MODBUS, 0 to 247 (decimal)
FUNCTION 8 bits
DATA Varies depending on commands.
CRC 16 bits
END 3.5-character time (Differs depending on baud rate. Refer to reception
judgement time.)
Response in normal status
The same message as a command is returned for single write command.
A part of a command message (6 bytes from the beginning) is returned for multiple write command.
Response in abnormal status
In case a parameter disabled to be processed is found in a command (except transmission error)
Slave address (unit number)
Function code + 80H
Error code
CRC
One of either 1, 2 or 3
Error code contents
1: Function code error
2: Device number error (out of range)
3: Device quantity error (out of range)
Reception done judgment time
The process for receiving a message completes when the time that is exceeding the time mentioned
below has passed after the final data was received.
Baud rate Reception done judgment time
2400 Approx. 13.3 ms
4800 Approx. 6.7 ms
9600 Approx. 3.3 ms
19200 Approx. 1.7 ms
38400 Approx. 0.8 ms
57600 Approx. 0.6 ms
115200 Approx. 0.3 ms
Note) The reception done judgment time is an approx. 32-bit time.
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