Rockwell Automation DAG6.5.8 APPLICATION GUIDE SCADA SYSTEM - Manual (Page 326)

Publication AG-UM008C-EN-P - February 2005
10-6 Using Dial-up Telephone Communication
To dial a modem from the processor, use an AWA instruction and store
the telephone number to be dialed in a string file element or string tag
via the programming software. In this example, when the B3:0/0 bit is
set, the processor sends the ASCII string atdt5551212 out the serial
port. This causes the modem to attempt to dial the number (5551212)
and establish the telephone link. To enter this type of rung into your
ladder logic, go to the Instruction Toolbar of your RSLogix
programming software and choose the AWA symbol under the ASCII
Control or ASCII Serial Port tab. The length of the string being sent is
0, which specifies the whole string. When the instruction is executed,
all characters in the string (ST20:0) will be sent. Use data monitor to
store the telephone number within the source address of the AWA.
Verify Connection to the Remote Modem
For PLC-5 and SLC processors, start a modem connection timer upon
triggering the dialing string and monitor the channel 0 lost modem bit
in the status file to determine when the connection is successful. (The
lost modem bit goes from a one to a zero when the connection is
established.) In a PLC-5 processor, the lost modem bit address is
S:17/5, while in the SLC 5/03, 5/04, and 5/05 processors, the address
is S:5/14.
For Logix processors, program an unconditional GSV instruction to
continually read the channel 0 diagnostic counters into a tag array.
Start a modem connection timer upon triggering the dialing string and
monitor the channel 0 Carrier Detect (CD) bit (bit 3 in word 1 of the
diagnostic counter tag array) until it becomes a 1 to determine when
the connection is successful.
For MicroLogix controllers, start a modem connection timer upon
triggering the dialing string and monitor the channel 0 CTS bit,
CS0:9/0, until it becomes a one to determine when the connection is
successful.
TIP
The number being dialed in this example is a local
number. If the number were long distance, the
number in the string file would have to include a 1
and the area code, for example: 14145551212. The
dialing string must be set to exactly what you would
send if you were dialing from a dumb terminal.