Rockwell RFX144V24-S23, Руководство дизайнера

Страница: 159 / 198

RFX144V24-S23 and RFX96V24-S23 Modem Designer’s Guide
1070 10-3
10.5 DAA REQUIREMENTS
To receive CND information, the modem monitors the phone line between the first and second ring bursts without causing
the DAA to go off hook in the conventional sense, which would inhibit the transmission of CND information by the local
central office. A simple modification to an existing DAA circuit (Figure 10-1) easily accomplishes the task.
With the addition of Q1 and K2, the DAA is AC-coupled to the phone line through the ring detect capacitor, C1, allowing the
CND signal to pass to the modem while blocking DC loop current that would place the line off hook.
10.6 MODEM REQUIREMENTS
Although the data signaling interface parameters match those of a Bell 202 modem, the receiving CPE need not be a Bell
202 modem. A V.23 1200 bps modem receiver may be used to demodulate the Bell 202 signal.
The ring detection circuit, combined with a “Ring Detection” firmware routine done by the host, allows the host to activate
and deactivate the CNDEN relay to monitor the telephone line for receiving the CND information.
After a valid ring is detected, the RI bit is set to indicate occurrence of the first ring burst to the host. The host waits for 250
ms of silence then activates the CNDEN line (see Figure 10-1) and configures the modem for CND reception as follows:
CONF = 22h
PDM = 1
SETUP = 1 and wait until SETUP = 0
Wait until CDET = 1
The received data is now available via DBUFF (10:0-7).
CNDEN must be deactivated by the host prior to the reception of the second ring burst.
10.7 APPLICATIONS
Flowcharts corresponding to the above process are shown in Figure 10-2.
Once CND information is received, the user may process the information in a number of ways.
1. The date, time, and calling party's directory number can be displayed.
2. Using a look-up table, the calling party's directory number can be correlated with his or her name and the name
displayed.
3. CND information can also be used in additional ways such as for:
a) Bulletin board applications,
b) Black-listing applications,
c) Keeping logs of system user calls, or
d) Implementing a telemarketing data base.
10.8 REFERENCES
For more information on Calling Number Delivery (CND), refer to Bellcore publications TR-TSY-000030 and TR-TSY-
000031.
To obtain Bellcore documents, contact:
Bellcore Customer Service
60 New England Avenue, Room 1B252
Piscataway, NJ 08834-4196
(201) 699-5800