7.10.4 Read Holding Registers (03 HEX)
Description
This function reads the contents of holding registers in the slave.
Query
The query message specifies the starting register and quantity of registers to be read. Register addresses start at zero, i.e. registers 1-4 are addressed
as 0-3.
Example: Read par. 3-03,
Maximum Reference, register 03030.
Field Name
Example (HEX)
Slave Address
01
Function
03 (read holding registers)
Starting Address HI
0B (Register address 3029)
Starting Address LO
05 (Register address 3029)
No. of Points HI
00
No. of Points LO
02 - (Par. 3-03 is 32 bits long, i.e. 2 registers)
Error Check (CRC)
-
Response
The register data in the response message are packed as two bytes per register, with the binary contents right justified within each byte. For each register,
the first byte contains the high order bits and the second contains the low order bits.
Field Name
Example (HEX)
Slave Address
01
Function
03
Byte Count
04
Data HI
(Register 3030)
00
Data LO
(Register 3030)
16
Data HI
(Register 3031)
E3
Data LO
(Register 3031)
60
Error Check
(CRC)
-
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