Rockwell Automation DAG6.5.8 APPLICATION GUIDE SCADA SYSTEM - Manual (Page 324)

Publication AG-UM008C-EN-P - February 2005
10-4 Using Dial-up Telephone Communication
Configure the Modems for MicroLogix 1100/1200/1500 Controllers
The MicroLogix channel 0 serial port does not support the DSR, CD or
DTR modem handshake signals. (The MicroLogix 1500 channel 1 does
support CD, but not DSR or DTR.) The only handshake signal from
the modem supported by the MicroLogix is Clear to Send (CTS).
Therefore, a different modem handshaking scheme is required when
using MicroLogix 1100/1200/1500 controllers to initiate dial-out
connections. Even when a MicroLogix 1100/1200/1500 channel 0 is
configured for no handshaking, it still monitors CTS. Therefore, RTS
and DTR must be ignored by the modem and CTS must be configured
in the modem to be on (or high) whenever a modem carrier from a
remote modem is being received and off (or low) otherwise. That
way, CTS can be used to determine when the modem connection has
been successfully established. The only way to hang up the
connection is to return the modem to command mode (typically by
sending the ASCII string ‘+++’ to the modem), and then sending an
ASCII ATH command.
The ASCII string to send to the modem that supports AT commands to
configure the RS-232 control signals to operate as described above is
as follows: AT &S0 &C1 &D0 &R2 Q1 E0 &W.
The ASCII string should be sent to the modem followed by carriage
return and line feed control characters. Note that the Q1 and E0
disable response codes and local character echo, and the &W saves
the configuration to the modem’s nonvolatile memory, if available.
See chapter 8 for example cable configurations for specific dial-up
modems.
Communicating Over the
Telephone Line
To communicate over the telephone line:
1. Initiate modem dialing.
2. Verify connection to the remote modem.
3. Transfer data back and forth.
4. Hang up the telephone link.