Rockwell Automation 1762-Lxxxx MicroLogix 1200 Programmable Controllers - Manual (Page 134)

Publication 1762-UM001G-EN-P - March 2011
E-4 Connect 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 (Data Set Ready, Carrier
Detect and Data Terminal Ready) are supported by
any MicroLogix 1200 controllers.