Data Exchange Between Modbus Tcp Master And I/O Modules - WAGO 750 Series Manual

72 • Fieldbus Controller 750-841
Data Exchange
Addressing Example:
Address calculation (depending upon the word address):
Bit address:
Byte address:
Dword address:

3.1.6.3 Data Exchange between MODBUS TCP Master and I/O Modules

The data exchange between the MODBUS TCP master and the I/O modules is
made via the Ethernet Fieldbus port using MODBUS TCP read and write
commands.
The controller handles four different types of process data with MODBUS
TCP:
•
•
•
•
The relationship between bits and words are defined in the table below:
Digital inputs/outputs
Prozess data word
Byte
Table 3.9: Allocation of Digital Inputs/Outputs to Process Data Word in Intel Format
word address (even numbers) / 2
or word address (uneven numbers) / 2, rounded off
Input words
Output words
Input bits
Output bits
16. 15. 14. 13. 12. 11. 10. 9.
Bit Bit
15 14
High-Byte
D1
word address .0 to .15
1. Byte: 2 x word address
2. Byte: 2 x word address + 1
Bit Bit Bit Bit Bit Bit
13 12 11 10 9 8
8. 7. 6. 5. 4. 3.
Bit Bit Bit Bit Bit Bit
7 6 5 4 3 2
Low-Byte
D0
WAGO-I/O-SYSTEM 750
ETHERNET TCP/IP
2. 1.
Bit Bit
1 0