Precautions - Mitsubishi Electric Q03UDVCPU User Manual

6.7

Precautions

(1) Send/receive packet
• When a message larger than 1460 bytes is sent from the external device using TCP, a packet may be
divided. As a result, data may not be received as one message with the predefined protocol function. Keep
the message less than 1460 bytes or use UDP.
• When data is received using TCP, separate data blocks that are sent successively may be combined at the
receiving side. Therefore, handshaking is required prior to communications.
(2) Predefined protocol setting
Power on or reset the CPU module, or turn on SM1355 (Predefined protocol setting check request) to enable the
written protocol setting data. If the written data are not enabled, the data may be changed unintentionally when
the CPU module is powered on or is reset.
(3) Device data
Data set by the predefined protocol function are communicated during the service processing. Therefore, if the
COM instruction is executed while b15 of SD778 (Refresh processing selection when the COM/CCOM instruction
is executed) is on, data communications are also performed at the execution of the COM instruction.
(4) Connection with different open systems
Even the connection for which the open system is set to "Socket Communication" in parameter can be reopened
as the predefined protocol after the connection is closed. Similarly, the connection for which the open system is
set to "Predefined Protocol" in parameter can be reopened as the socket communication after the connection is
closed.
However, if the connection for which the open system is set to "Socket Communication" in parameter is reopened
as the predefined protocol after completion of closing, the status storage and protocol cancellation are not
possible since the start device to store the predefined protocol operation status cannot be specified.
CHAPTER 6 DATA COMMUNICATIONS USING THE PREDEFINED PROTOCOL
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