ECOLAB Versatronic Modbus Beschreibung Seite 140

Modbus over Ethernet
Example: Reading n words
Reading the IP address of the device. The address used in the example is 10.10.1.69.
Since each octet of the IP address is saved in a word, it is necessary here to read 4
words, that is, 8 bytes.
See also the Modbus example in
Query:
MBAP header
0x0001
2 bytes
Transaction ID
Assignment of
response to
request
(consecutive
numbering)
Response:
MBAP header
0x0001 0x0000
2 bytes 2 bytes
Transacti Protocol
on ID ID
Assign- For
ment of Modbus
response always
to query 0x00
417102397 Rev. 1-10.2019
Ä Chapter 3.4.1 'Reading n words' on page 18.
0x0000 0x0006
2 bytes 2 bytes
Protocol ID Length
Length of the
request in
For Modbus bytes starting
always with (incl.)
0x0000 "Unit ID"; 6
bytes here
(0x06)
Modbus telegram (without slave address and CRC)
0x000B 0xFF
2 bytes 1 byte
Length Unit ID
Length of
response
in bytes
For TCP
(incl.)
always
"Unit ID";
0xFF
in this
case 11
bytes
Modbus telegram (without slave
address and CRC)
0xFF 0x03
1 byte
1 byte Unit ID Function code
Function code
for "Reading n
For TCP words"
always FF or
255
0x03 0x08 0x000A
1 byte
1 byte
Number
Function
of bytes
code
read
IP address consisting of 4 octets
Function
code for 8 bytes
"Reading were read
10.
n words"
40
0x19C9 0x0004
2 bytes 2 bytes
address First Number of
word words
First word of 4 words
IP address to should be
be read read
0x000A 0x0001 0x0045
8 bytes
1 word per octet
4 octets × 2 bytes = 8 bytes
10. 1. 69