Allen-Bradley micrologix 1500, User Manual

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Publication 1764-UM001A-US-P
Understanding Communication Protocols E-7
Using Modems with
MicroLogix 1500
Programmable
Controllers
The types of modems that you can use with MicroLogix 1500 controllers include
dial-up phone modems, leased-line modems, radio modems and line drivers.
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 multi-drop modem connections, or for point-to-point modem connections
that require RTS/CTS handshaking, use DF1 Half-Duplex slave protocol.
Dial-Up Phone Modems
Some dial-up phone line modems support point-to-point Full-Duplex
communications. A MicroLogix 1500 controller, on the receiving end of the
dial-up connection, can be configured for DF1 Full-Duplex protocol with or
without handshaking. The modem connected to the MicroLogix controller should
support auto-answer. The MicroLogix 1500 Series B processors (1764-LSP and
1764-LRP) support ASCII out communications. There fore, they can cause the
modem to initiate or disconnect a phone call.
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
multi-drop topology supporting Half-Duplex communications between three or
more modems.
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.
IMPORTANT
Never attempt to use DH-485 protocol through modems under
any circumstance.
NOTE
All MicroLogix 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
1500 controllers. MicroLogix 1500 1764-LRP processors also
support DCD (Data Carrier Detect)
AB Spares