Specifications

Head Station STL-ETH1 (Ethernet) Ethernet
Quick Start Guide for the MELSEC STlite Series 4 - 9
Data Exchange between MODBUS/TCP Master and I/O Modules
Data exchange between the MODBUS/TCP Master and the I/O modules is conducted using the MOD-
BUS functions implemented in the controller by means of bit-by-bit or word-by-word reading and
writing routines.
There are 4 different types of process data in the controller:
–Input words
–Output words
–Input bits
– Output bits
Access by word to the digital I/O modules is carried out in accordance with the following table:
Output can be read back in by adding an offset of 0200 H to the MODBUS address.
Register functions start at address 1000 H . These functions can be addressed in a similar manner with
the MODBUS function codes that are implemented (read/write).
The specific register address is then specified instead of the address for a module channel.
Digital Inputs/Outputs
16. 15. 14. 13. 12. 11. 10. 9. 8. 7. 6. 5. 4. 3. 2. 1.
Process data word
Bit
15
Bit
14
Bit
13
Bit
12
Bit
11
Bit
10
Bit
9
Bit
8
Bit
7
Bit
6
Bit
5
Bit
4
Bit
3
Bit
2
Bit
1
Bit
0
Byte
High byte D1 Low byte D0
Tab. 4-3: Allocation of digital inputs and outputs to process data words
NOTE Data > 256 words can be read back by using the cumulative offset!
All output data greater than 256 words and, therefore located in the memory range 6000
H to
62FC
H , can be read back by adding an offset of 1000 H to the MODBUS address.
Fig. 4-9: Data exchange between MODBUS Master and I/O modules
MODBUS master
Word 0
Inputs
0000
H
I/O modules
Outputs
00FF
H
PII PIO
6000H
62FCH
0000H
(0200H)
00FF
H
(02FFH)
6000
H
(7000H)
62FC
H
(72FCH)
PII: Process Input Image
PII: Process Output Image
Programmable Fieldbus
Controller