Chapter 5 Communication
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5.2 Modbus communication protocol
Function code 03 (0x03): read one or more registers
Inquiry frame
Name
Device
address
Function
code
Initial
address
Number of
data
CRC
Data
Addr
0x03
M
N
CRC16
Length
(bytes)
1
1
2
2
2
Response frame (normal response)
Name
Device
address
Function
code
Return
byte
Return
data
CRC
Data
Addr
0x03
N * 2
Data
CRC16
Length
(bytes)
1
1
1
N * 2
2
Special Notes
Inquiry frame: the number of data indicates the number of read registers, the data
range (1 ~ 50)
Response frame: the high byte of each register comes first, and the low byte
comes afterwards. (floating point data is arranged in the order of floating-point
format)
Example
Read pH value (example measurement mode is pH)
Inquiry: 01 03 00 01 00 02 95 CB
Response: 01 03 04 40 E0 00 00 EE 05
It shows that the pH value was read successfully. The current value is 7.00pH
(floating point format 4321).
