Yaskawa MP920 Communications Module - Manual (Page 176)

7 218IF Module
7.6.2 Communications Ladder Logic Programming
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When using the TCP protocol in no protocol (through) mode, note the following points:
Because the TCP protocol is a byte-stream protocol, complicated byte-stream processing must gener-
ally be created in the Controller’s ladder logic program.
As a general rule, with the TCP protocol, the transmission data will be stored as far as possible in a
send buffer, and as much data as possible should be transmitted in the same packet.
For example, when data is transmitted continuously, it is not clear from the timing of the transmissions
how may data items have been transmitted in one packet.
With no protocol, there is no field showing the send data length. Therefore, the receiving end does not
know how much data has been transmitted from the remote station.
It is best to avoid such situations.
In any case, when using the TCP protocol, be sure that the TCP packets are not transmitted continu-
ously. Either leave an interval (at least 1 second is recommended) between each packet, or use a com-
mand/response application protocol. This will remove the need to create complicated byte-stream
processing.
7.6.2 Communications Ladder Logic Programming
This section gives examples of ladder logic programming for message transmission and
reception with 218IF devices.
IMPORTANT