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Chapter 7 Communication function
7-5
7.1.3 User defined Function Block (SND_MSG, RCV_MSG)
Users are required to use Cnet’s dedicated TX/RX Function Blocks for the definition of communication frames via
Frame Editor and for communication in PLC program via the defined frames. SND_MSG Function Block is applied for
transmitting and RCV_MSG Function Block is applied for receiving. Insert the communication library first into GMWIN
project as in the case of other communication Function Blocks, in order to use Function Block for user definition.
[Figure 7.4] shows how to insert the communication library in the project screen. Choose file of COMMUNI.*FB per
CPU type to insert into its correspondent project.
[Figure 7.4] library insertion into project
1) Transmission Function Block : SND_MSG(Send Message)
Figure on the right shows transmission Function Block, SND_MSG to transmit
frames composed for transmission along with user’s input data to variable via
a defined channel of Cnet I/F module. The same frame name in ‘FNAM’ area
in the Function Block must be downloaded to Cnet I/F module prior to
execution of the receive Function Block. Since the frames are classified in
accordance with their names by the Function Block when transmission frames
are being composed in Frame Editor, normal communication can not be
possible if names of the frames are identical. Besides, same number of SDx
with the number of ARRAY variables is required if ARRAY variables are used
in the Frame Editor. [Table 7.2] shows how to use I/O variables of SND_MSG
Function Block.