Rockwell Automation 1770-HT8 SMART TRANSMITTER - Manual (Page 55)

Installing the Smart Transmitter Interface
Products
Chapter 2
2-30
DTE Controlled Answer: these unattended modems are directly
connected to the phone lines. The Smart Transmitter Interface serves as
the data terminal equipment to control the modem via the DTR, DSR
and DCD signals. The Smart Transmitter Interface incorporates timeouts
and tests to operate these types of modems properly.
Auto-Answer: these modems have self-contained timeouts and test, and
can answer and hang up the phone automatically.
The Communications Controller has no means of controlling an auto-dial
modem, but it can be used in conjunction with a separate auto-dialer.
If your application requires the use of leased lines, you will probably not
be using a dial-up modem. Some non-dial-up modems are designed to
assert a continuous DSR signal, a situation that would leave the
Communications Controller waiting forever for communication with the
modem.
To avoid this, construct your cable with the jumper indicated in
Figure 2.28.
Figure 2.28
Connection between a Communications Controller and a Modem
(Other than a DialĆup Modem)
1
TXD 2
RXD 3
RTS 4
CTS 5
DSR 6
GND 7
DCD 8
DTR 20
MODEM
2 RXD
3 TXD
4 RTS
5 CTS
6 DSR
7 GND
8 DCD
20 DTR
Shield
90030
Jumper
Communications Controller