7 Communication Using MC Protocol
49
FX3U-ENET-ADP User's Manual
1
Introduction
2
Specification
3
System
Configuration
4
Installation
5
Wiring
6
Introduction of
Functions
7
Communication
Using
MC Protocol
8
The Operation
of GX Works2
9
Troubleshooting
A
List of Special
Devices
7.2 Data Communication Function
7.2.3 Access Timing on the PLC Side
The following diagram illustrates the access timing on the PLC side when an external device accesses the
PLC via the Ethernet adapter.
1) A command message is transmitted from the external device to the PLC side.
2) Upon receiving a command message from the external device, the Ethernet adapter on the PLC side
sends a data read/write request to the PLC according to the content of the command.
3) The PLC reads/writes data according to the request from the external device at the time of executing the
sequence program's END instruction, and passes the processing result to the Ethernet adapter.
4) Upon receiving the processing result from the PLC, the Ethernet adapter sends a response message
including the processing result to the external device that originated the request.
*1. The ACK response shown in the diagram is sent/received between the Ethernet adapter and the
external device respectively when access via the Ethernet adapter is performed by TCP/IP
communication. It is different from the response to the processing requested by the external device in
the command message (the processing result).
When access via the Ethernet adapter is performed by UDP/IP, the ACK response indicated by *1 is
not sent.
Regarding the scan time of the PLC
• While the PLC is performing a required command, access command to the Ethernet adapter and the PLC
is processed during every END processing.
(The scan time becomes longer according to the amount of time it takes to process the command.)
• When multiple external devices issue access requests to the Ethernet adapter at the same time, the
processing requested from the external devices may have to wait for multiple END processing executions
depending on the timing of the requests.
7.2.4 PLC setting for performing data communication
Set the following contents in GX Works2, write parameters to the main unit, and turn OFF and ON the power
of the Ethernet adapter (PLC) to enable data communication using the MC protocol.
1) Operational settings (Refer to Section 6.6, Section 8.1)
2) Open settings (Refer to Section 6.11, Section 8.2)
*1
*1
STEP 0
END STEP 0 END STEP 0 END STEP 0 END
External device
Read/write command
(command)
Ethernet adapter
ACK
ACK
Reply to the command
(response)
4)1)
3)2)
PLC
END processing END processing END processing
Processing of the command from the external device
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