Rockwell Automation 1775-KA PLC-3 Communication Adapter Module User Manual - Manual (Page 25)

Installation
Chapter 2
2Ć13
Pinout
The necessary RS–232–C port connections are described in Table 2.D
below:
Table 2.D
RS-232-C Port Connections
Signal at the
1775-KA Abbreviation Pin Input/Output
chassis/shield drain 1
transmitted data TXD 2 Output
received data RXD 3 Input
request to send RTS 4 Output
clear to send CTS 5 Input
data set ready DSR 6 Input
transmitted data return TXDRET 7/14
data carrier detect DCD 8 Input
data terminal ready DTR 20/11 Output
received data return RXDRET 25/13
TXD (transmitted data) caries serialized data. It is output from the
RS–232 connector.
RXD (received data) is serialized data input to the RS–232 connector.
RXD and RXDRET are isolated from the rest of the circuitry on the
module.
RTS (request to send) is a request from the RS–232 connector to the
modem to prepare to transmit. It typically turns the data carrier on.
When you select the full duplex mode RTS is always asserted. When
you select the half duplex mode RTS is turned on when the module has
permission to transmit; otherwise it is off.
CTS (clear to send) is a signal from the modem to the RS–232
connector that the carrier is stable and the modem is ready to transmit.
The module will not transmit until CTS is true. If CTS is turned off
during transmission, the module will stop sending until CTS is restored.
DTR (data terminal ready) is a signal from the RS–232 connector to the
modem to connect to the phone line (that is, “pick up the phone”). The
module will assert DTR all the time except during the phone hangup