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Method of control via Modbus protocol
4.10 Function code
„ Reading from a holding register(s) (03h)
This function code is used to read a register (16 bits). Up to 16 successive registers (16×16 bits) can be read.
Read the upper and lower data at the same time. If they are not read at the same time, the value may be invalid.
If multiple holding registers are read, they are read in order of register addresses.
Example of read
Read the rotation speed Nos. 0 and 1 in the operation data of slave address 1.
Description
Rotation speed No.0 (upper)
Rotation speed No.0 (lower)
Rotation speed No.1 (upper)
Rotation speed No.1 (lower)
• Query
Field name
Slave address
Function code
Register address (upper)
Register address (lower)
Data
Number of registers (upper)
Number of registers (lower)
Error check (lower)
Error check (upper)
• Response
Slave address
Function code
Number of data bytes
Value read from register address (upper)
Value read from register address (lower)
Value read from register address+1 (upper)
Data
Value read from register address+1 (lower)
Value read from register address+2 (upper)
Value read from register address+2 (lower)
Value read from register address+3 (upper)
Value read from register address+3 (lower)
Error check (lower)
Error check (upper)
−16−
Register address
0480h
0481h
0482h
0483h
Data
01h
Slave address 1
03h
Reading from a holding register(s).
04h
Register address to start reading from
80h
00h
Number of registers to be read from the starting register address
(4 registers=0004h)
04h
44h
Calculation result of CRC-16
D1h
Field name
Value read
Corresponding decimal
0000h
0064h
0000h
0FA0h
Description
Data
Description
01h
Same as query
03h
Same as query
08h
Twice the number of registers in the query
00h
Value read from register address 0480h
00h
00h
Value read from register address 0481h
64h
00h
Value read from register address 0482h
00h
0Fh
Value read from register address 0483h
A0h
E1h
Calculation result of CRC-16
97h
100
4000
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