FX602 Consumer Microcircuits Limited, FX602 Datasheet - Page 15

• Manufacturer Part Number: FX602
• Description: Calling Line Identifier
• Manufacturer: Consumer Microcircuits Limited

Calling Line Identifier
FX602
Figure 8c : Bellcore System signals (without ring)
1.6.2
'Off-Hook' Operation
Introduction
CIDCW (Calling Identity on Call Waiting) is a telephone service which identifies a waiting caller without
interrupting your current call. It eliminates the ‘blind spot’ in traditional Call Waiting by giving a telephone user
the informed choice of whether or not to take the incoming call.
To support CIDCW, the circuits of Caller ID compatible telephone equipment and adjunct ‘boxes’ must detect a
subtle CPE Alert Signal (CAS), injected into phone conversations. The CAS is transmitted by the Central Office
to initiate a CIDCW transaction and consists of a 80ms burst of simultaneous 2130Hz and 2750Hz tones.
CAS detection accuracy is very important because both missed and false signal detection is evident and
annoying to telephone users. Missed signal detection causes Caller ID information to be lost, false signal
detection produces a disruptive tone which is heard by the far end caller. Because the CAS signals must be
detected in the presence of conversations which both mask and masquerade as the tone signals, this function
is very difficult to accomplish correctly.
This application note describes the use of the FX602 for accurate CAS detection, providing better CIDCW
performance than other solutions. The FX602's <1µA ring detect supply current, 3 to 5 volt supply range, and
16 pin package also offer significant advantages in battery life and final product size.
Overview
A successful CIDCW transaction as described in Bellcore SR-TSV-002476 consists of a sequence of actions
between the CPE (Customer Premises Equipment - e.g. a telephone) and the Central Office as indicated in
Figure 9a.
1998 Consumer Microcircuits Limited
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D/602/7