Rockwell Automation 1775-KA PLC-3 Communication Adapter Module User Manual - Manual (Page 26)

Installation
Chapter 2
2Ć14
sequence. Some modem will not respond to DTR until the phone rings,
while others will always pick up the phone whether it is ringing or not.
DSR (data set ready) is a signal from the modem to the RS–232
connector that the phone is off–hook. (It is the modem’s answer to
DTR). The module will not transmit or receive unless DSR is true. If
the modem does not properly control DSR, or if no modem is used,
DSR must be jumpered to an RS–232 high signal at the RS–232
connector. (It can be jumpered to DTR).
DCD (data clear ready) is a signal from the modem to the RS–232
connector 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 RS– 232 connector unless DCD is true. In
the full duplex mode the module will not transmit unless DCD is true.
If the modem does not properly control DCD, or if a modem is not
being used, DCD must be jumpered to DTR at the RS–232 connector.
TXDRET (transmitted data return) is the return signal for TXD. It is
connected to module logic ground through a resistor.
RXDRET (received data return) is the return signal for RXD. It is
connected to the isolated receiver, and is isolated from all other
circuitry on the module.
Connections To The RS–232 Port
Connection to the RS–232 port of the 1775–KA can be one of two types:
Short line (50 feet or less)
Isolated long line (between 50 and 7,000 feet)
For short lines, the connection may be either direct or through modems.
You connect an intelligent, RS–232–C compatible device to an interface
module by attaching a cable to both the device and to the module socket
labeled RS– 232–C CHANNEL. The RS–232–C device may be another
Allen–Bradley communication interface module or another
manufacturer’s device. For a standard RS–232–C connection, the cable
should be no longer than 50 feet. If your RS–232–C device has an
Allen–Bradley line driver/receiver, you may use a cable up to 7,000 feet
long.
If you want to connect the 1775–KA module to a 1771–KG or
1771–KE/KF module through the RS–232–C channel, use the cabling
pinout diagram (Figure 2.8) to construct your own cable.