Modbus TCP server
51
COM465IP-COM465DP_D00216_02_M_XXEN/03.2017
6.2.4.3 Reference value on channel 2
The following reference value is stored in this channel:12.34 A
Tab. 6.5: Reference data stored in channel 2
6.2.4.4 Explanation of how to access floating point values
The test value 12.34 can be read out via Modbus TCP using Modbus function 0x04 at the address
0x0014. The test value has a size of 2 words.
Proceed as follows:
1.
Interpreting both words as unsigned integer values should result in the following values:
Word 1 with address 0x14: unsigned integer value => 16709 (0x4145)
Word 2 with address 0x15: unsigned integer value => 28836 (0x70A4)
2. Determine the correct byte or word swap
There are four different combinations of swapping. The only correct value is 12.34.
All swapping combinations are represented in the following table.
Word 0x14 0x15 0x16 0x17
HiByte LoByte HiByte LoByte HiByte LoByte HiByte LoByte
0x41 0x45 0x70 0xA4 0x00 0x03 0x00 0x4A
Floating point value AT&T R&U Description
12.34 No/No Ampere Overcurrent
Hex value
sequence
Word 1 Word 2
Floating point
value
Byte 1 Byte 2 Byte 3 Byte 4
CORRECT
A
41
B
45
C
70
D
A4
12.34
Word swapping
C
70
D
A4
A
41
B
45
4.066E+29
Byte swapping
B
45
A
41
D
A4
C
70
3098.27
Word and byte
swapping
D
A4
C
70
B
45
A
41
-5.21E-17
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