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Chapter 7 Communication function
7-97
7.3.3 How to use dedicated Function Block
Ex.1 describes how to communicate between Cnets via dedicated Function Block.
1) Example of use
Ex.1 describes how to program for communication between station 1 as master and 2 & 3 stations as slaves via
RS-485 channel between Cnet I/F modules in the system configuration shown as in [Figure 7.16]. It is supposed
that master station 1 reads/saves 10 bytes of %MB100 area data of station 2 to its %MB0 area, and reads/writes
40 bytes of data from its %MB20 to %MB200 area of station 3. Next is for this mapping data TX/RX.
Master station
Slave
station
Class
Master
area
Slave
area
Data
length
Station 1 Station 2 Reading %MB0 %MB100 10 Bytes
Station 1 Station 3 Writing %MB20 %MB200 40 Bytes
[Figure 7.16] RS-485 communication structure between Cnet I/F modules
2) Basic setting items
[Figure 7.16] shows system configuration composed of RS-485 multi-drops between Cnets. For the system
communication between Cnet I/F modules, RS-422 operation mode of 3 stations shall be set to dedicated mode with
the stations numbers set to station No. 1,2,3 respectively as not repeated. Since all 3 stations are in communication
via the same communication line, all basic parameters such as communication speed, data, stop bit, etc. shall be set
identical. Next is basic setting items for communication between 3 stations.
Station No. Cnet Ver. Mode switch Basic parameters Master/Slave
Station1 Surely Ver.2.0
3(dedicated stand-
alone mode)
Master operation
Station2 Irrelevant to Ver.
3(dedicated stand-
alone mode)
Slave operation
Station 3 Irrelevant to Ver.
3(dedicated stand-
alone mode)
RS-422
basic parameters of 3
stations shall be set
identical
Slave operation
Master(v2.0)
(Slave)
(Slave)
Dedicated mode
Dedicated mode
Dedicated mode
RS-485 Interface