EM78P813

8-bit OTP Micro-controller

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* This specification is subject to change without notice.

55

2004/8/19

(V1.6)

VII.10 CALL WAITING Function Description

CWTIP

Filter

Vdd/2

Detection

block

Voltage

reference

GAIN

FSK

demodulator

TIP

RING

-

+

CAS

DATA

/CD

Fig.33

Call Waiting Block Diagram

Call Waiting service works by alerting a customer engaged in a telephone call to a new incoming call. This way

the customer can still receive important calls while engaged in a current call. The CALL WAITING DECODER can

detect CAS(Call-Waiting Alerting Signal 2130Hz plus 2750Hz) and generate a valid signal on the data pins.

The call waiting decoder is designed to support the Caller Number Deliver feature, which is offered by regional

Bell Operating Companies.

In a typical application, after enabling CW circuit (by R5 page3 bit3 & bit4 ) this IC receives Tip and Ring

signals from twisted pairs. The signals as inputs of pre-amplifier, and the amplifier sends input signal to a band pass

filter. Once the signal is filtered, the Detection block decodes the information and sends it to RE page2 bit7 . The

output data made available at RE CAS bit.

The data is CAS signals. The CAS is normal high. When this IC detects 2130Hz and 2750Hz frequency, then

CAS pin goes to low.