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MELSEC-F
OVERVIEW1
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1.2 Features of the Ethernet Module
(1) Data communication using MC protocol (Details are explained in
Chapter 8 and Chapter 9)
Using MC protocol, the device data of the PLC can be read from/written to the
host system.
This protocol is a passive protocol that communicates data solely according to
the requests from the host system. It does not require a sequence program for
data communication after a connection is established.
(2) Communication using fixed buffers (Details are explained in
Chapters 6 and 7)
With communication using fixed buffers, a maximum of 1023 words of arbitrary
data can be sent or received between PLCs or between the PLC and an arbitrary
device.
An Ethernet module is provided with 8 fixed buffer data areas each with 1023
word storage space, and each is assigned as either a sending or receiving buffer
for an arbitrary device.
Since communication using MC protocol is passive, communication using fixed
buffers is an active protocol. Data can be sent from the PLC side to another PLC
and an arbitrary device when equipment errors occur or when some specified
conditions are satisfied.
External device
Local station
Command
Response
Receive/send
Receive/send
External device
External device
Local station