Data Exchange Between Modbus Master And I/O Modules; Data Exchange Between The Modbus Master And I/O Modules - WAGO -I/O-SYSTEM 750 User's Installation And Configuration

34 • Fieldbus coupler 750-342
Data exchange
3.1.5.3

Data exchange between MODBUS master and I/O modules

The data exchange between the MODBUS master and the I/O modules is ma-
de by the implemented MODBUS functions in the coupler with reading and
writing in bits or bytes.
The controller handles four different types of process data:
•
•
•
•
The word for word access to the digital input and output modules is made in
accordance with the following table:
Digital inputs/
outputs
Process data
word
Table 3.3: Allocation of digital inputs/outputs to process data word acc. Intel format
The outputs can be read back by adding 0x0200 to the MODBUS address.
The register functions made available in the coupler, can be addressed by the
MODBUS master along with the implemented MODBUS function codes
(read/write). To this effect, the individual register address is entered in place of
the address of a module channel.
Fig. 3-10: Data exchange between the MODBUS master and I/O modules
Input words
Output words
Input bits
Output bits
16. 15. 14. 13. 12. 11. 10. 9.
Bit
15
MODBUS master
0x000
PII
0x0FF
Inputs
I/O modules
Fieldbus Coupler
Bit Bit Bit Bit Bit Bit
14 13 12 11 10 9
0x000
(0x200)
PIO
0x0FF
(0x2FF)
Outputs
8. 7. 6. 5. 4.
Bit Bit Bit Bit Bit Bit
8 7 6 5 4 3
PII = Process Input
Image
PIO = Process Output
Image
Modular I/O System
ETHERNET TCP/IP
3. 2. 1.
Bit Bit Bit
2 1 0
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