Rockwell Automation DAG6.5.8 APPLICATION GUIDE SCADA SYSTEM - Manual (Page 141)

Publication AG-UM008C-EN-P - February 2005
Configuring SLC 5/03, 5/04, and 5/05 Processors 4-3
Using Modems that Support
DF1 Communication
Protocols The types of modems that you can use with SLC processors include
dial-up phone modems, leased-line modems, radio modems and line
drivers. For point-to-point full-duplex modem connections, use DF1
full-duplex protocol. For general point-to-multipoint modem
connections, use DF1 half-duplex master and slave protocols. In this
case, one (and only one) of the other devices must be configured for
DF1 half-duplex master protocol. For most radio modem connections,
use DF1 radio modem protocol.
Dial-up Phone Modems
Dial-up phone line modems support point-to-point full-duplex
communications. Normally, an SLC processor on the initiating or
receiving end of the dial-up connection, will be configured for DF1
full-duplex protocol with the control line parameter set for
Full-Duplex Modem. See page 4-5 for details on the operation of the
RS-232 modem control signals when Full-Duplex Modem is selected.
See Chapter 11 for further details on using SLC processors in dial-up
modem applications.
When an SLC processor is the initiator of the dial-up connection, use
one of the ASCII write instructions to send out the AT dial-up string
(for example ATDT 555-1212). The status file modem lost bit (S:5/14)
provides the feedback that the connection has been successfully
made. To hang up the connection, use the ASCII AHL instruction to
temporarily lower the DTR signal.
Leased-Line Modems
Leased-line modems are used with dedicated phone lines that are
typically leased from the local phone company. The dedicated lines
may be point-to-point topology supporting full-duplex
communications between two modems or in a point-to-multipoint
topology supporting half-duplex communications between three or
more modems. In the point-to-point topology, configure the SLC
processor for DF1 full-duplex protocol with the control line parameter
set to Full-Duplex Modem. In the point-to-multipoint topology,
configure the SLC processors for DF1 half-duplex master or slave
protocol with the control parameter set to Half-Duplex Modem
without Continuous Carrier. See page 4-6 for details on the operation
IMPORTANT
Do not attempt to use DH-485 protocol through
modems under any circumstance.