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MELSEC-F
FIXED BUFFER COMMUNICATION (WITH THE NO PROCEDURE
CONTROL METHOD)
7
7 - 9
7.5 Programming
This section explains the programming method when the Ethernet module
communicates with an external device using fixed buffers and the no-procedure
control method.
7.5.1 Precautions when creating programs
(1) In order to communicate using the fixed buffers, the initial processing and the
connection open processing must be completed.
(2) The contents of the parameter settings have been loaded into the Ethernet
module when the Ethernet module open completion signal (BFM#20480
corresponding bit) switches from off to on.
(3) The data length (byte count) is established using the instruction for no procedure
communication.
If the send data length exceeds this range at data sending, a communication
error occurs and the data is not be sent.
(4) Reading or writing to the buffer memory using fixed buffer communication.
• When sending data
Write the send data to the buffer memory (BFM#1664 to #9855).
Write "0001
H" in BFM#1610 to #1617 before sending the data.
• When receiving data
Check that data has been received (BFM#1610 to 1617: "0001
H") and read out
the received data (BFM#1664 to #9855) to the PLC.
(5) The following should be observed when using a connection opened by UDP.
• External devices can be switched by modifying the setting values in the
communication address setting area of the communication parameter setting
area before sending/receiving data. Thus, data can be sent to multiple external
devices sequentially. When sending/receiving, make sure to switch between
external devices properly so that no communication problems occur.
(6) Message data length is not included in a packet when communicating with the no
procedure.
The Ethernet module stores the size of the received message (packet) in the
receive data length storage area and turns on the fixed buffer receiving status
signal (BFM#20485 corresponding bit).
It is recommended to employ a check system, such as including the data length
and data type code in the application data of a message, so that the byte count
and data type in the application data can be identified by the receiving side.