Request PDU
Function code
1 byte
0x04
Starting address
2 bytes
0x0000 to 0xFFFF
Quantity of Input Registers
2 bytes
0x0000 to 0x007D
Response PDU
Function code
1 byte
0x04
Byte count
1 byte
2 x
N*
Input register value
N*
x 2 bytes
*N = Quantity of registers
Exception Response PDU
Error code
1 byte
0x84 (=0x04 + 0x80)
Exception code
1 byte
01 or 02 or 03 or 04
Here is an example of a request to read the
parameter (input registers 3 and 4).
Request
Response
Field name
(Hex)
Field name
(Hex)
Function
04
Function
04
Starting address Hi
00
Byte count
04
Starting address Lo
02
Register 3 value Hi
00
Quantity of Input Reg. Hi
00
Register 3 value Lo
00
Quantity of Input Reg. Lo
02
Register 4 value Hi
2F
Register 4 value Lo
F0
As you can see in the table, the
(input registers 3 and 4) contains the value 00 00 2F F0 hex, i.e. 12272 in
decimal notation.
MAN RD6 MB E 1.1
Modbus® interface
56 of 92
RD6 Modbus®