1.3 Overview of Communication Functions
1.3.4 General-Purpose Communication
Overview of function
• General-purpose communication is used when PLC executes communication in accordance
with the command specifications of the partner device.
• Formulation and sending of command messages to the partner device, and reception
processing of responses from the partner device, are performed by the user program.
Sending/receiving of data with an external device is executed via given operation memory
(e.g. data register).
• Data are sent by setting message/data in a given data register in accordance with the
partner device, and executing GPSEND command.
• Data received from the partner device are temporarily saved in the buffer. Based on the
reception done flag, GPRECV command is executed and the received data are copied into a
given operation memory. The received data can be converted into numerical data, etc. as
necessary, by the user program.
• The data size that can be sent or received in a single communication is up to 16,372 bytes
per connection.
(Note 1) When a dedicated header is not attached, the size is up to 16,384 bytes.
(Note 2) In the case of connection with our PLC FP2 ET-LAN unit, the maximum size is 8,192 bytes.
FP7 CPU External device
Ethernet LAN
IP XXXXXX
IP XXXXXX
Send/receive message/data
Message/data
Send
Receive
Operation
memory
Message/data
Applications of general-purpose communication
This is used for communication with devices made by differing manufacturers that have
dedicated communication protocols.
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