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DID Commands
The DID modem uses *D commands to configure the modem's DID features. The modem must be configured for the
proper protocol, digit format, digit time out, digit report format, and number of digits. This configuration is determined
by the company from which the DID line is ordered and the setup used by the phone company. The DID configuration
parameter settings of the modem can be viewed as part of the report of the AT&V command and can be stored with
AT&X0 command.
Command:
*DS
Start Protocol
Values:
n = 0, 1, 2 or 3
Default:
0
Description:
There are three different types of DID start protocols: Wink, Immediate, and Delay Dial.
In the Wink Start protocol, the central office closes the loop and draws current. The modem
senses the current draw and will reverse the DC polarity for a short pulse to sign that it sees
the incoming call and is ready to accept the DID digits.
Delay Dial is the same as Wink Start with the exception that the length of the reverse pulse
is not defined. When the DID modem senses the current draw, it will reverse the DC voltage
until it is ready to receive the DID digits.
On an Immediate Start DID line, the central office closes the loop for a short time and then
sends the DID digits without waiting for a response from the DID modem.
After the central office sends the DID digits all three lines operate the same way. The
modem will reverse the DC polarity to signal the beginning of the call and the central office
will open the channel to the caller and begin billing. When the call is completed, the DID
modem will return the DC voltage to normal polarity and the central office will open the
circuit.
While the modem is monitoring the DID line for current draw, it is also monitoring the POTS
line for incoming rings.
*DS0
*DS1
*DS2
*DS3
Command:
*DT
Wait for Digit Time-Out Time
Values:
DTn - n=0-30 seconds
Default:
0
Description:
This command is used to configure the time between each digit the modem will wait. If the
modem has not received the proper number of digits when the timer expires, it will report the
digits it has received so far and move on to the answering sequence described in the *DN
command.
Command:
*DD
Digit Format
Values:
0, 1, 2
Default:
0
Description:
This command is used to configure the modem for the format the central office will send the
incoming digits. At this time, only DTMF is supported.
*DD0
*DD1
*DD2
Command: *DN
Number of DID Digits Expected
Values:
0-7
Default:
0
Description:
This command is used to configure the modem for the expected number of digits from the
central office (the central office will send the last few digits of the called number). When the
proper number of digits are received, the modem will pass the digit information to the host
computer. After passing the digits the modem will answer the incoming call if S0 is greater
than 0. Otherwise the modem will wait for the host computer to issue an ATA command.
Multi-Tech Systems, Inc. AT Commands Reference Guide (PN S000272E)
Disables DID detection of incoming DID calls (DC voltage still applies to DID line)
Wink Start
Immediate Start
Delay Dial
DTMF
Pulse
MF (MultiFrequency)
Chapter 1 – AT Commands
25
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