Written By: Jerry Mills
DTR Dialing Cookbook
Using External Multi-Tech Modems
A method for automatically dialing a number stored in the modems memory by turning DTR on. DTR (Data Terminal Ready) is a signal sent from the computer, mux, printer or terminal to the modem. DTR has an indicator light on the modem labeled TR (Terminal Ready), when lit, TR indicates DTR is present from the computer,mux, printer or terminal. When TR is not lit, DTR is turned off. In order for DTR to work it is important that the modem see DTR go from an off state (Low), to an on state (High), this is usually done by turning off the computer, mux, printer or terminal attached to the modem and then turning it back on. This act will toggle DTR and signal the modem to dial the number stored in memory.
NOTE: If doing DTR dialing with a PC it is important to note that DTR is normally turned off until you start a communications software such as Windows terminal or WIN95 hyperterminal. It is not neccessary to turn off the PC to toggle DTR, usually all that is required is to exit the software and then start the software up again
1. Connect a PC or laptop running a communications software package such as Windows
terminal, to the modems RS232 interface. (The 25 pin female connection in the back)
- OR -
Connect an ordinary CRT Terminal with a straight thru cable.
2. Setup the modem using the following strings:
ATE1Q0 enable command echo and modem responses so you can
see what you are typing.
AT&F8 this enables the modems factory default rom
AT&F reads in the factory defaults
ATM3E0Q1&C1&D2&E5&E7$BA0$SB19200T&W0 -->enter entire string
M3 sets speaker to be on while dialing then turns off
E0 disables command echoing
Q1 disables response codes
&C1 enables normal carrier operation
&D2 enables normal DTR operation i.e. modem hangs up when low
&E5 use XON/XOFF flow control
&E7 XON/XOFF characters are passed thru the modem
$BA0 Turn off Autobaud
$SB19200 sets serial port speed to 19.2k baud
T modem uses tone dialing
&W0 stores configuration in NVRAM (memory)
NOTE: Once you have entered this string you will not be able to see what you type!
To review your settings use the ATL5, L6, AND L7 to see the current settings.
3. Store the number to be dialed into the modems memory
ATDT<the number to dial>N0
To view the number entered use ATL. This will list the stored number for your review.
4. Tell the modem to do DTR dialing
Example: AT$D1 (Turns on DTR dialing) or AT$D0 (Turns off DTR dialing)
5. Store configuration changes with the following command: