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5-6
Chapter 5. Modbus Communication (RTU Mode)
5 - 3
Description of Commands
Function 03 (multiple data read command)
Function 03 is the command for reading multiple data records.
The command and normal response formats are shown in the table.
Note
•
Error termination code (p. 5-4)
(for details of error response)
z
Send command format
Frame structure
Number
of bytes
Description
Address
1
Device address
Function
1
03 (0x03)
Data
Data address
2
Data address (upper byte
→
lower byte)
Number of data
records
2
Number of data records (upper byte
→
lower byte)
CRC check
2
Check code (lower byte
→
upper byte)
z
Normal response format
Frame structure
Number
of bytes
Description
Address
1
Device address
Function
1
03 (0x03)
Data
Data size
1
Number of data bytes that were read
(= 2 × number of data records)
1st data record
2
Read data (upper byte
→
lower byte)
to
(more read data)
nth data record
2
Read data (upper byte
→
lower byte)
CRC check
2
Check code (lower byte
→
upper byte)
Examples:
Sent message: Read 2 data records from data address 2001 (0x07D1)
Device address
Function code
Data address
Number of
data records
CRC
01H
03H
07H
D1H
00H
02H
95H
46H
Normal response: When the data that was read is 0 (0x0000) and 1 (0x0001)
Device address
Function code
Data size
Data 1
Data 2
CRC
01H
03H
04H
00H 00H 00H 01H 3BH F3H
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