EM78808
8-bit Micro-controller
/POVD
2.2V /POVD reset voltage
2.2V Power on reset voltage
Sleep mode current (VDD=5V)
1
0
No
Yes (2.2V)
Yes (2.2V)
No
1uA
15uA
VII.9 CALL WAITING Function Description
TIP
DATA
/CD
FSK
demodulator
RING
GAIN
CWTIP
-
+
CAS
Detection
block
Filter
Vdd/2
Voltage
reference
Fig.26 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 IOC5 page0 bit4 CWPWR) 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 R3
register bit7 . The output data made available at R3 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.
______________________________________________________________________________________________________________________________________________________
* This specification is subject to change without notice.
8/1/2004 (V3.1)
48
ELAN [ ELAN MICROELECTRONICS CORP ]
