Message Format And Control Procedure - Mitsubishi Electric FX3U-ENET-ADP User Manual

FX -ENET-ADP User's Manual
3U
2) When an external device writes data to the PLC
External
device side
PLC side
a) Area C indicates transmission from the external device to the PLC.
b) The program of the external device is generated so that the data is transmitted sequentially from left to
right. (For example: in case of area C, data should be sequentially sent starting from the header.)
When the PLC receives a command message from an external device, it completes processing of the data in
area A/C, then sends a response message and waits for the next command message (neutral state).
7.3.2

Message format and control procedure

This section explains the message format and control procedure.
1) Message format
This section explains the message format for transmission between the Ethernet adapter and an external
device.
The communication data consists of "header" and "application data" as shown below.
Header
a) Header
The header for TCP/IP or UDP/IP is used. The user does not need to specify it; the Ethernet adapter
attaches it.
b) Application data
The application data is largely divided into "subheader" and "text" as shown below.
- The subheader represents command/response and the setting value is predetermined.
- The text contains the request data (command) and response data (response) for each function and
this data is determined by the prescribed format (for a more detailed description, refer to Section 7.5
and later).
c) Format in the application data field
- Communication in ASCII code
External
device
side
PLC side
- Communication in binary code
External
device
side
PLC side
(Command message)
Area C
Application data
Application data
Subheader Text (command)
Differs depending
2 bytes
on function
Application data
Text (command)
Subheader
Differs depending
1 byte
on function
7 Communication Using MC Protocol
7.3 Message Formats and Control Procedures
(Response message)
Differs depending on
function and
normal/abnormal
2 bytes
completion
Subheader
Application data
Differs depending on
function and
normal/abnormal
1 byte
completion
Subheader
Application data
Text (response)
Text (response)
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A