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APPENDIX
Appendix 7.2.5 How to connect the communication module to an external device and
precautions on specifying control by signals
App - 34
In the following, some precautions on specifying the control by signals using an
interface connection between the communication module and an external device are
given using the RS-232C interface as an example.
(1) When only the RS (RTS) and CS (CTS) control signal lines are
looped back on the communication module side
Communication
module
(Signal name)
RD(RXD)
SD(TXD)
ER(DTR)
SG
DR(DSR)
RS(RTS)
CS(CTS)
If the RS (RTS) control is disabled, data can be received from the external device
but data cannot be sent to the external device.
In order to send data, turn the RS (RTS) control signal ON using processing code
32 of the ZCNTL instruction.
(2) When only the ER (DTR) and DR (DSR) control signal lines are
looped back on the communication module side
Communication
module
(Signal name)
RD(RXD)
SD(TXD)
ER(DTR)
SG
DR(DSR)
RS(RTS)
CS(CTS)
If the ER (DTR) control is disabled and DR (DSR) control is enabled, data can be
received from the external device but data cannot be sent to the external device.
In order to send data, disable the DR (DSR) control.
RS-232C
Connector
RS-232C
Connector
MELSEC-Q
External
device
Connector
External
device
Connector
App - 34
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