Rockwell Automation 1770-KF2 Data Highway or Highway Plus Interface Module User Manual - Manual (Page 35)

Installation
Chapter 3
3-11
The definitions of the above signals are:
TXD carries serialized data. It is an RS-232-C standard output from
the module.
RXD is RS-232-C standard serialized data input to the module.
RTS is a request from the module to the modem to prepare to transmit.
With full-duplex protocol, RTS is always asserted. With half-duplex
protocol, it is turned on when the module has permission to transmit;
otherwise it is off. It conforms to RS-232-C specifications.
CTS is a signal from the modem to the module that indicates the carrier
is stable and the modem is ready to transmit. The module will not
transmit until CTS is on. If CTS is turned off during transmission, the
module will stop transmitting until CTS is restored. It conforms to
RS-232-C specifications.
DTR is a signal from the module to the modem to connect to the phone
line (i.e., “pick up the phone”). The module will assert DTR all the
time except during the phone hang-up sequence. Modems built to
American standards will not respond to DTR until the phone rings.
Some European modems will always pick up the phone, whether it is
ringing or not. The KF2 module will not work with these types of
European modems. DTR conforms to RS-232-C specifications.
DSR is a signal from the modem to the module that indicates the phone
is off-hook. (It is the modem’s answer to DTR.) The module will not
transmit or receive unless DSR is on. If the modem does not properly
control DSR, or if no modem is used, DSR must be jumpered to a high
signal at the module’s asynchronous connector. (It can be jumpered to
DTR.) DSR conforms to RS-232-C specifications.
DCD is a signal from the modem to the module to indicate that the
carrier from another modem is being sensed on the phone line. It will
not be asserted unless the phone is off-hook. Data will not be received
at the asynchronous connector unless DCD is on. With full-duplex
protocol, the module will not transmit unless DCD is on. If the modem
does not properly control DCD, or if a modem is not being used, DCD
must be jumpered to DTR at the module. DCD conforms to RS-232-C
specifications.
TDA is the transmitted data signal for RS-422-A output from the
module.
TDB is the differential return signal for TDA for transmitting
RS-422-A data.
RDA is the RS-422-A data input to the module.
RDB is the differential return signal for RDA.
If you are connecting a KF2 module to an RS-232-C compatible device
(e.g., modem or computer), then you must mount the module within
50 cable-feet of that device. For such applications, the module’s GND