Siemens SIMATIC ET 200SP Equipment Manual page 17

RS232 signals
The table below shows the meaning of the individual RS232 accompanying signals.
Table 2- 2 Signals of the RS232 interface
Signal Designation
TXD
Transmit Data
RXD
Receive Data
RTS Request To Send
CTS
Clear To Send
DTR Data Terminal Ready
DSR Data Set Ready
RI
Ring Indicator
DCD Data Carrier Detect
CM PtP communications module (6ES7137-6AA01-0BA0)
Equipment Manual, 03/2021, A5E03790792-01
Meaning
Transmit data; transmit cable logically held to "1" by communications module in idle
state.
Receive data; receive cable logically held to "1" by communication partner in idle state.
Request to send
RTS set to "ON": communications module ready to send; signals to the communication
partner that there is data ready to send
RTS set to "OFF": communications module does not send
Clear to send
CTS set to "ON": Signals "clear to send" to the communication partner
CTS set to "OFF": Signals "Not clear to send" to the communication partner
DTR set to "ON": Communications module switched on, ready for operation
DTR set to "OFF": Communications module not switched on, not ready for operation
DSR set to "ON": Communication partner signals "ready for operation"
DSR set to "OFF": Communication partner not switched on, not ready for operation
Incoming call when connecting a modem
Carrier signal when connecting a modem. The communication partner signals with a
high level that it detects incoming data on the cable.
Product overview
2.3 Properties of the interfaces
17