Black Box MD1640A, MD1641A manual Dialing a Stored Number N, DTR Dialing $D

CHAPTER 5: Command Mode

This command would be used only if you had already reached a busy number after executing a normal dial command. You simply enter A: (you need not enter AT, nor do you need to hit RETURN), and the modem will redial the number for you. If you again reach a busy signal, it re-dials again and again until it no longer detects a busy signal. You can stop the Series II Modem from re-dialing by pressing any key.

Another method used to cause the modem to redial a phone number continuously is to enter a colon : at the end of the phone number. The result is the same as if you had entered A: after personally observing that the number was busy on the first dialing attempt. Using the colon in the dialing string is a step saver.

Dialing a Stored Number N

A telephone number that you have stored in the Series II Modem’s number memory may be automatically dialed by entering ATNn where n = 0, 1, 2, 3, 4, 5, 6, 7, 8 or 9. For example, a number stored at N3 would be dialed by entering ATN3 and RETURN. Do not include the letter D in this command, or the stored number will be erased (also see Section 5.4.3., on Phone Number Memory Commands).

DTR Dialing $D

An alternate method of causing the Series II Modem to automatically dial is DTR Dialing. Data Terminal Ready (DTR) is a signal that comes into the modem from the terminal or computer to which it is connected, on pin 20 of the RS232C interface. In DTR dialing, the modem automatically dials a stored number as soon as it receives a high DTR Signal. The DTR dialing method is popular in synchronous appli- cations.

To activate DTR Dialing, enter AT$D1 and hit RETURN. The modem dials the phone number stored in the N0 location of memory when it receives a high DTR signal. DTR must remain high for the duration of the call, until disconnect. To deactivate DTR dialing, enter AT$D0 and hit RETURN.

Note that when you use DTR Dialing in a synchronous application, you need to make sure DIP-Switch #8 is in the UP position to disable V.25bis Command mode.

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