7-6
Chapter 7. Modbus RTU Communication Functions
7 - 3
Description of Commands
z
Multiple data read command (03H)
Reads the continuous data addresses in hexadecimal notation.
z
z
Instruction message
Specifies the first data address and the number of data items. The structure of the
instruction message is as follows.
(1) Station address
(2) Function code
(3) First data address
(4) Number of data
(5) Check code (CRC)
z
z
Response message
The structure of the response message is as follows.
•
Example in normal status
(1) Station address
(2) Function code
(3) Number of items read × 2 (number of bytes)
(4) Read data 1
(5) Read data 2
(6) Check code (CRC)
•
Example in error status
(1) Station address
(2) Function code (In case of an error, 1 is set for the MSB of the function code in
a send message. In this example, 84 responds to undefined 04.)
(3) Exception code
(4) Check code (CRC)
(2)
(1)
(3)
(4)
0AH 03H 03H E9H 00H 02H 14H
(5)
C0H
(2)
(1)
(3)
(4)
0AH 03H 04H 03H 01H 00H 03H
(5)
(6)
51H 76H
(2)
(1)
(3)
0AH 84H 01H F3H 02H
(4)
