Siemens SIMATIC CP 340 User Manual page 19

RS 232C signals
The table below shows the meaning of the RS 232C accompanying signals.
Table 1- 5 RS 232C interface signals
Signal Designation
TXD Transmitted Data
RXD Received Data
RTS Request To Send
CTS Clear to send
DTR Data terminal ready
DSR Data Set Ready
RI Ring Indicator
DCD Data carrier detect
PtP coupling and configuration of CP 340
Manual, 04/2011, A5E00369892-03
Meaning
Transmitted data; transmission line is maintained at logic "1" by the communication
processor in idle state.
Received data; receive line must be maintained at logic "1" by communication
partner.
RTS "ON": Communication processor is ready to send.
RTS "OFF": Communication processor is not sending.
Communication partner can receive data from the communication processor. The
communication processor expects this signal in response to RTS "ON".
DTR "ON": Communication processor is active and ready for operation.
DTR "OFF": Communication processor is not active and not ready for operation.
DSR "ON": Communication partner is active and ready for operation.
DSR "OFF": Communication partner is not active and not ready for operation.
Incoming call when connecting a modem
Carrier signal when connecting a modem
Product Description
1.4 Properties of the serial interface
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