52
Function Code 0x03 Read Holding Registers
Function Code
0x03 is intended for reading multiple registers
(16-bit values). Using FC 0x03 the measurement values can
be polled for the Web-IO depending on which
Start Address
is
used.
1. Byte
16 Bit / Word
High Byte
Low Byte
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
2. Byte
3. Byte
16 Bit / Word
High Byte
Low Byte
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
4. Byte
8 Bit / Byte
Byte
7 6 5 4 3 2 1 0
7. Byte
Protocol ID
Transaction ID
5. Byte
16 Bit / Word
High Byte
Low Byte
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
6. Byte
Length
Unit ID
Function Code
XX
XX
00
00
01
00
06
8 Bit / Byte
Byte
7 6 5 4 3 2 1 0
8. Byte
03
9. Byte
16 Bit / Word
High Byte
Low Byte
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
10. Byte
20
00
11. Byte
16 Bit / Word
High Byte
Low Byte
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
12. Byte
XX
XX
Start Address
Number of
Registers
Start Address
Specifies the address to start reading the registers.
Number of Registers
Here the number of registers to read is transmitted.
The Web-IO replies with the following packet: