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MELSEC-F
WHEN COMMUNICATING DATA USING THE MC PROTOCOL9
9 - 3
9.1.2 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
module and an external device.
The communication data consists of "header" and "application data" as shown
below.
(a) Header
The header for TCP/IP or UDP/IP is used. The user does not need to specify
it; the Ethernet module 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, see sections 9.3 and later).
(c) Format in the application data field
• Communication in ASCII code
• Communication in binary code
NOTE
When communicating in the MC protocol, the user does not need to specify a
response for a command from an external device; the Ethernet module generates it
and then responds.
Header
Application data
Application data
External
device
side
PLC side
Subheader Text (command)
2 bytes
Differs depending
on function
2 bytes
Differs depending on
function and
normal/abnormal
completion
Subheader
Text (response)
Application data
Application data
External
device
side
Subheader
Text (command)
1 byte
Differs depending
on function
PLC side
1 byte
Differs depending on
function and
normal/abnormal
completion
Subheader
Text (response)
Application data