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4 MESSAGES OF SERIAL COMMUNICATION MODULE
4.1 Types and Purposes of Messages
4 MESSAGES OF SERIAL COMMUNICATION
MODULE
This section explains the specifications of the messages of MC protocol and access range when connecting with serial
communication from an external device.
4.1 Types and Purposes of Messages
The messages of MC protocol can be classified as shown in the following table depending on the supported device and its
intended purpose.
Formats and codes
There are five formats for the message that can be used for serial communication module.
Set the format with the communication protocol setting of Engineering tool.
Communication using binary code shorten the communication time since the amount of communication data
is reduced by approximately half as compared to the one using ASCII code.
Frame
This section explains the types and purposes of the frames (data communication messages) used by the external device to
access the supported devices using MC protocol.
The frames for serial communication modules are as follows:
Setting value Format Code of communication data Remarks Reference
1 Format 1 ASCII code Page 29 Format 1
2 Format 2 ASCII code Format with block number appended Page 30 Format 2
3 Format 3 ASCII code Format enclosed with STX and ETX Page 31 Format 3
4 Format 4 ASCII code Format with CR and LF appended at the end Page 32 Format 4
5 Format 5 Binary code Can be used by 4C frame. Page 33 Format 5
Frame Features and purposes Compatible message format Format
4C frame Accessible from external devices with the maximum
access range.
Dedicated protocols for MELSEC-QnA series serial
communication modules (QnA extension frame).
Formats 1 to 5
3C frame These message formats are simplified compared to the
4C frame.
Data communication software for MELSEC-QnA series
programmable controllers can be used.
Dedicated protocols for MELSEC-QnA series serial
communication modules (QnA frame).
Formats 1 to 4
2C frame Dedicated protocols for MELSEC-QnA series serial
communication modules (QnA simplified frame).
1C frame These frames have the same message structures as
when accessing the CPU module using an MELSEC-A
series computer link module.
Data communication software for MELSEC-A series
programmable controllers can be used.
Dedicated protocols for MELSEC-A series computer link
modules
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