Rockwell Automation 1770-KF3 DH-485 Communication Interface User Manual - Manual (Page 16)

Installing the KF3
Chapter 2
2Ć8
Cabling for the RS-232C connector of the KF3 will vary depending on
your application. The pinouts for this connector are given in Table 2.B.
Table 2.B
RSĆ232C Connector Pinouts
Signal Abbreviation Direction Pin No. Meaning
Chassis Ground - - 1 The cable shield must be connected to chassis ground at one
end only.
Transmit Data TXD Output 2 RSĆ232C serialized data output from the module.
Receive Data RXD Input 3 RSĆ232C serialized data input to the module.
Request to Send RTS Output 4 A request from the module to the modem to prepare to
transmit. With fullĆduplex protocol, RTS is always asserted.
With halfĆduplex protocol, it is turned on when the module has
permission to transmit, otherwise it is off.
Clear to Send CTS Input 5 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.
Data Set Ready DSR Input 6 A signal from the modem to the module that indicates the
phone is offĆhook. It is the modem's answer to DTR. The
module will not transmit or receive unless DSR is on. If
the modem does not control DSR properly, DSR must be
jumpered to a high signal at the module. (It can be jumpered
to DTR.)
Signal Ground GND - 7 Signal ground - a reference point for the data signals.
Data Carrier Detect DCD Input 8 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 offĆhook.
Data will not be received by the KF3 unless DCD is on. With
fullĆduplex protocol, the module will not transmit unless DCD
is on. If the modem does not control DCD properly, DCD must
be jumpered to DTR at the module.
Data Terminal Ready DTR Output 20 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 hangĆup sequence.
Modems built to North American standards will not respond
to DTR until the phone rings. The KF3 module will not work
correctly with modems which always pick up the phone upon
receiving DTR, whether the phone is ringing or not.
RSĆ232C Cabling
Considerations