Rockwell Automation DAG6.5.8 APPLICATION GUIDE SCADA SYSTEM - Manual (Page 325)

Publication AG-UM008C-EN-P - February 2005
Using Dial-up Telephone Communication 10-5
Initiate Modem Dialing
To initiate dialing from a PLC-5, SLC, Logix or MicroLogix processor,
use the ASCII write with append instruction (AWA). This instruction
lets you send an ASCII string out the serial port with no protocol
framing added, despite the fact that the serial port has been
configured for DF1 protocol. By sending the dialing command string
to the modem, the modem then dials the telephone number given,
which lets the two modems establish a connection. Figure 10.3 is a
sample ladder logic rung used to trigger the AWA instruction to send
the dialing string (stored in a data file) to a modem, as it appears in a
PLC-5, SLC or MicroLogix processor.
Figure 10.3 AWA Instruction
Figure 10.4 shows the telephone number stored in file ST20. In a
Logix processor, the telephone number would be stored in a string
tag.
Figure 10.4 Store the Telephone Number