Publication 1747-RM001G-EN-P - November 2008
13-84 SLC Communication Channels
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 radio modem connections, use DF1 Radio Modem. 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. Do not attempt to use
DH-485 protocol through modems under any circumstance.
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 13-86 for
details on the operation of the RS-232 modem control signals when
Full-duplex Modem is selected.
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 in a
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 line parameter set to Half-duplex Modem without
Continuous Carrier. See page 13-87 for details on the operation of the RS-232
modem control signals when Half-duplex Modem without Continuous Carrier
is selected.
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