GN-9371_2_3 User Manual
Page 84 of (110)
G-series GN-9371_2_3 PIO Rev. 1.02.docx
A.3.3 (0x03) Read Holding Registers
This function code is used to read the contents of a contiguous block of holding registers in a remote device.
The Request PDU specifies the starting register address and the number of registers.
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.
•
Request
Field name
Example
RTU
Start of Frame
-
t1-t2-t3
Slave Address
0x07
0x07
Function Code
0x03
0x03
Starting Address Hi
0x08
0x08
Starting Address Lo
0x00
0x00
Quantity of Register Hi
0x00
0x00
Quantity of Register Lo
0x02
0x02
Error Check (CRC/LRC)
-
0xC6, 0x0D
End of Frame
-
t1-t2-t3
•
Response
Field name
Example
RTU
Start of Frame
-
t1-t2-t3
Slave Address
0x07
0x07
Function Code
0x03
0x03
Byte Count
0x04
0x04
Output Register #0 Hi
0x11
0x11
Output Register #0 Lo
0x22
0x22
Output Register #1 Hi
0x33
0x33
Output Register #1 Lo
0x44
0x44
Error Check (CRC/LRC)
-
0x2D, 0xC6
End of Frame
-
t1-t2-t3
-
In case of address 0x0800, 0x0801 output register value: 0x1122, 0x3344.