Considerations When Connecting C24 - Mitsubishi Electric MELSEC IQ-R series Reference Manual

Considerations when connecting C24

The following shows the considerations when performing data communication between C24.
Conditions that C24 transmission sequence becomes initial status
The transmission sequence of C24 becomes initial status under the following conditions.
• When turning the power ON, changing the status of reset switch on the front of the CPU, and switching modes.
• When the transmission of a response message for the command message reception is completed.
• When a transmission sequence initialization request is received.
• When the CD signal turns OFF while performing data communication by setting the "CD terminal check enable" in the full-
duplex communication of RS-232.
Abnormal response from C24
An abnormal response to the external device using MC protocol is issued when an error is detected in the request sent to the
connected station (host station). Therefore, an abnormal response may be issued while sending request from the external
device in the full-duplex communication.
Replacement of other station CPU modules to communicate with
C24 imports and retains the information of other station CPU modules after started up.
When replacing the other station CPU module to perform data communication after starting up C24, reboot the C24 if the
model name of the CPU module is changed. (Reset the programmable controller of the connected station (host station)/CPU
reset).
Framing error on external device
A framing error may occur on the external device when nothing is sent from C24 to the external device via RS-422/485.
 Q Corresponding Serial Communication Module User's Manual (Basic)
 MELSEC-L Serial Communication Module User's Manual (Basic)
 MELSEC iQ-R Serial Communication Module User's Manual (Application)
Skip reading data until C24 sends either STX, ACK, or NAK on the external device.
Before the data communication, check the C24 interface specification written in the following manuals.
 Q Corresponding Serial Communication Module User's Manual (Basic)
 MELSEC-L Serial Communication Module User's Manual (Basic)
 MELSEC iQ-R Serial Communication Module User's Manual (Startup)
Installation of multiple C24s
When multiple external devices that are connected to each C24 request access to the CPU module at the same time, the
CPU module decides the order of access.
The access priority order cannot be set by user.
3 COMMUNICATION PROCEDURE
3.2 Considerations
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