Publication 1762-UM001D-EN-P - March 2004
E-4 Connecting to Networks via RS-232 Interface
• radio modems
Radio modems may be implemented in a point-to-point
topology supporting either Half-Duplex or Full-Duplex
communications, or in a multi-drop topology supporting
Half-Duplex communications between three or more modems.
MicroLogix 1200 also supports DF1 Radio Modem protocol.
• line drivers
Line drivers, also called short-haul modems, do not actually
modulate the serial data, but rather condition the electrical
signals to operate reliably over long transmission distances (up
to several miles). Line drivers are available in Full-Duplex and
Half-Duplex models. Allen-Bradley’s AIC+ Advanced Interface
Converter is a Half-Duplex line driver that converts an RS-232
electrical signal into an RS-485 electrical signal, increasing the
signal transmission distance from 50 to 4000 feet (8000 feet
when bridged).
For point-to-point Full-Duplex modem connections that do not
require any modem handshaking signals to operate, use DF1
Full-Duplex protocol with no handshaking. For point-to-point
Full-Duplex modem connections that require RTS/CTS handshaking,
use DF1 Full-Duplex protocol with handshaking.
For radio modem connections, use DF1 Radio Modem protocol,
especially if store and forward capability is required.
For general multi-drop modem connections, or for point-to-point
modem connections that require RTS/CTS handshaking, use DF1
Half-Duplex slave protocol. In this case, one (and only one) of the
other devices must be configured for DF1 Half-Duplex master
protocol.
IMPORTANT
Never attempt to use DH-485 protocol through
modems under any circumstance.
TIP
All MicroLogix 1200 controllers support RTS/CTS
modem handshaking when configured for DF1
Full-Duplex protocol with the control line parameter
set to Full-Duplex Modem Handshaking or DF1
Half-Duplex slave protocol with the control line
parameter set to “Half-Duplex Modem”. No other
modem handshaking lines (i.e. Data Set Ready,
Carrier Detect and Data Terminal Ready) are
supported by any MicroLogix 1200 controllers.
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