14 6619-2202
 
PSTN 
Network
Application examples

…  TDW-33 connected to TDW-33 with DTR signal call

DTR
DSR
DCD
Relay
External
application
10 kohm
May be required in harsh environments.

Configure the units

AT&F Set the unit to factory default
AT&W Store default settings

Set up the connection – The dialling modem

AT&Z0=nnn Store the number of the remote modem in the dialling TDW-33
AT&S0 Set DSR signal always high (if this signal is used to trig the DTR)
AT&B1 Activates automatic DTR dialling if DTR switches from low (OFF) to high 
(ON) 
AT&W Save settings
Switch DTR from 
OFF to ON
The modem will now dial the phone number stored in the first location  of 
the telephone number table (AT&Z0=<nnn>)

Set up the connection – The answering modem

ATA Enter the answer command when RING comes from the network or set up 
ATS0=1 to auto answer on 1 RING signal (or more than 1)
NOTE:  If no valid DTR signal can be provided by external application, the modems 
DSR signal can be used to trig the transmission. Connect the DSR signal via 
a relay, or other potential free contact, to the DTR signal. A 10 kohm pull 
down resistor should also be connected between the DTR and a signal that 
is always low e.g. the DCD.