Multi-Tech Systems MT2834BA Series Dial Phone Number Provided CRN Command, DTR Dialing $D Command

Appendix D - V.25bis Operation

Dial Phone Number Provided (CRN) Command

The CRN command permits the dialing of the phone number immediately following it (from the command line). It is similar to the D command, except that the number is first checked against the Delayed Number and Forbidden Number list. If permitted, depending on the country regulations in effect, the number will then be dialed. For example, if you enter CRN7859875 and hit RETURN, your modem will check the two lists. If the number is on the Delayed Numbers list, you can dial that number again after t minutes have passed. If the number is on the Forbidden list, a CFIFC message will be displayed.

You can use various commands from the AT command set within the CRN command line to facilitate the dialing process, such as P, T, or : for pulse dialing, tone dialing and wait for dial tone. V.25bis supports “smart” dialing.

To dial a phone number, enter CRNdd...dd where dd...dd is the phone number, which can be up to 20 characters long using any character on the telephone pad (0 through 9, *, #, P, T, and :). Some additional dialing characters may be available, based on country regulations.

Listing Delayed Phone Numbers (RLD) Command

When a phone number is dialed by a CRN command and a connection is not made, the number is entered in the modem's V.25bis Delayed Number list along with the number of retry attempts. Any further dialing attempts will be delayed some amount of time (determined by the regulations of each country). While the delay is in progress, the modem will give a DLC indication. The list contains eight numbers. When filled, the next number failing “bumps” off the oldest number on the list onto the Forbidden Number list. Numbers on the Delayed Number list that succeed in a connect attempt are removed. If a certain number of failed attempts occur (the number of failed attempts is specified by each country), the number is entered into the V.25bis Forbidden Phone Number List. Forbidden phone numbers cannot be dialed at all. To list the phone numbers on the V.25bis Delayed Phone Number List, enter RLD and hit RETURN.

Listing Forbidden Phone Number (RLF) Command

Those phone numbers that have failed to connect the required number of times as specified by country regulations are removed from the Delayed Number list and entered onto the V.25bis Forbidden Number list. Numbers on the Forbidden Number list cannot be dialed at all for some maximum amount of time (specified by country regulations). In some countries, the time might be one hour, and in others the number may never be dialed again. The forbidden list is eight numbers long, with the newest number replacing the oldest if the memory is full. To view the Forbidden list enter RLF and hit RETURN.

Disregard or Connect to Incoming Calls (DIC or CIC) Command

The Disregard or Connect to Incoming Calls commands are used for Auto-Answer operations. Depending on the country regulations, your modem will wait some amount of time or number of rings before answering the call. During that time, you can stop the modem from answering the call by entering the DIC (Disregard Incoming Calls) command. CIC (Connect to Incoming Calls) command will cause your modem to answer the call (either reversing the effect of a DIC command or simply have your modem answer the call immediately without waiting the regulation time before answering).

DTR Dialing ($D) Command

DTR Dialing is an alternate method of causing the modem to automatically dial a number. Data Terminal Ready (DTR) is a signal that comes into the modem from the terminal or computer to which it is connected via pin 20 of the RS-232 interface. In DTR Dialing, the modem will automatically dial a stored number as soon as it receives a high DTR signal. The DTR Dialing method is popular when using the modem in synchronous applications.

To enable DTR Dialing, enter command AT$D1 and hit Return. The modem will now dial the phone number you have stored as N0 when it receives a high DTR signal.

DTR must remain high for the duration of the call, until disconnect. To disable DTR Dialing, enter the command AT$D0 (or AT$D) and hit RETURN.

When you use DTR Dialing, be sure that DIP-Switch #1 is in the UP position, so that DTR is not forced on. In addition, when using DTR Dialing in a synchronous application, be sure that DIP-Switch #8 is in the UP position to disable V.25bis Command mode.

Multi-Tech Systems, Inc. MT2834BA/BL Series User Guide 110