Rockwell Automation 1770-KF2 Data Highway or Highway Plus Interface Module User Manual - Manual (Page 38)

Installation
Chapter 3
3-14
The module can be connected to standard American dial-up modems and
some European modems. Other European standards specify that the DTR
signal will make the modem answer the phone whether it is ringing or not,
causing the phone always to be “busy.” Do not use the module with any
type of modem that answers the phone when DTR is asserted, even while
waiting for a call.
The types of dial-up network modems that you can use are:
Manual: These are typically acoustically coupled modems. The
connection is established by human operators at both ends, who insert
the handsets into couplers to complete the connection.
DTE-Controlled Answer: These unattended modems are directly
connected to the phone lines. The module serves as the data terminal
equipment to control 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
and 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.
Connection to Another Communication Module
To learn about a direct RS-232-C communication link with a 1771-KE,
-KF, or -KG module, refer to Figure 3.8. To construct the cable, use a
25-pin female connector at the KF2 end and a 15-pin male connector at
the other end.
To provide a direct RS-232-C link with a 1773-KA or a 1775-KA module,
Figure 3.9, use a 25-pin female connector at the KF2 and a 25-pin male
connector at the KA module.
Use Belden 8723 or equivalent cable (available from Allen-Bradley under
Cat. No. 1778-CR). Connect the cable shield at one end only. You can
make the cable up to 50 feet long.