Rockwell Automation 1747-KE,D17476.12 DH-485/RS-232C Interface Module - Manual (Page 17)

Publication 1747-UM005B-EN-P - March 2006
Overview 1-5
Use a Modem with Your
Interface Module The module can be connected to most types of dial-up network or
direct connect modems.
The type of modems you can use are:
• Manual - typically acoustically-coupled modems. A person on
each end of the phone line establishes the connection. They
then insert the handsets into an acoustic coupler to complete the
connection.
• DTE controlled answer - these unattended modems are attached
directly to the phone lines. The interface module acts as the
Data Terminal Equipment (DTE), which controls the modem via
the DTR, DSR, and DCD signals. The module incorporates
timeouts and tests to properly operate these types of modems.
• Auto answer - these modems have self-contained timeouts and
tests. They can answer and hang up the phone automatically.
The module has no means of controlling an auto-dial modem,
but it can be used in conjunction with a separate auto-dialer.
• Direct connect - these modems connect to a dedicated, leased
phone line and remain active at all times.
Use DF1 Protocol and Your
Module RSLinx software supports DF1 communications directly from your
computer’s serial communication port. Connecting a modem to this
port lets you to call remote networks and control them as if you were
connected locally.
DF1 Protocol
IMPORTANT
Some modems are designed to respond to the DTR
signal by answering the phone whether it is ringing
or not. Since the module asserts DTR at all times
(except during the hang-up sequence), the phone
appears to be busy at all times. Do not use the
interface module with any type of modem that
answers the phone as soon as DTR is asserted.
Interface Module
(1747-KE)
DF1 Protocol
DF1 Protocol
Modem
Modem
1747-C13 Cable
DF1