EM78815
8-Bit Microcontroller
7.10 Call Waiting Function Description
TIP
DATA
/CD
FSK
demodulator
RING
GAIN
CWTIP
-
+
CAS
Detection
block
Filter
Vdd/2
Voltage
reference
Fig.28 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
Alert 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 the CW circuit (by R5 Page 3 Bit 3 & Bit 4 ) this
IC receives Tip and Ring signals from twisted pairs. The signals as inputs by the 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 Page 2 Bit 7.
The output data is made available at RE CAS bit.
The data is CAS signals. The CAS is normal high. When this IC detects a 2130Hz
and a 2750Hz frequency, the CAS pin goes to low.
64 •
Product Specification (V2.4) 02.17.2006
(This specification is subject to change without further notice)
ELAN [ ELAN MICROELECTRONICS CORP ]
