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MELSEC-F

FIXED BUFFER COMMUNICATION (WITH THE PROCEDURE EXIST 

CONTROL METHOD)

6

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6.5 Programming

This section explains the programming method when the Ethernet module 
communicates with an external device using fixed buffers and the procedure exist 
control method.

6.5.1 Precautions when creating programs

(1) In order to communicate using the fixed buffer, 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 (word count) is established using the instruction for procedure 

exist communication control method.
If the send data length exceeds this range at data sending, a communication 
error occurs and the data is not sent. 

(4) Reading or writing to the buffer memory using fixed buffer communication.

• Data sending

Write the send data in the buffer memory (BFM#1664 to #3711).
Write "0001

H

" in BFM#1610, #1611 to send the data.

• Data receiving

Check the data received (BFM#1610, #1611: "0001

Hs

") and read the received 

data to the PLC (BFM#1664 to #3711).
After reading out, write "0002

H

" in BFM#1610, #1611 to send the response.

(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) For data (command) transmission, the next data (command) should be after the  

data commnication is complete (such as after receiving a response) for the 
transmission of the previous data (command).