Calling Line Identifier
MX602 - PRELIMINARY INFORMATION
13
The British Telecom Tone Alert signal consists of simultaneous 2130Hz and 2750Hz tones. The 'Chan Seize' signal
consists of a '1010..' FSK bit sequence in all cases.
IDLE 2
IDLE 2
≥ 100mS
< 4.8Sec
≥ 45mS
< 4.8Sec
88-110mS
80-262mS 45-75mS
≤ 2.5Sec
>200mS
SIGNALING
TONE
ALERT
CHAN
MARK
SEIZE
MESSAGE
RINGING
Line
reversal
RD
RT
IRQ
ZP
MODE
DET
RXD
Note: IDLE 1 + IDLE 2 ≤ 5 sec
Figure 13: British Telecom System Signals
5.2 MX602 CIDCW (Calling Line Identity on Call Waiting) Operation
5.2.1 Introduction
CIDCW 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), a dual tone injected into phone conversations. The CAS is transmitted by the central office to
initiate a CIDCW transaction consisting of an 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 tone signals must be detected in the presence of conversations which both mask
and masquerade as the tone signals, this function is very difficult to accurately achieve.
This application note describes the use of the MX602 for CIDCW CAS detection. The MX602’s 1µA ring detect supply
current, 3.3 to 5.5 volt supply range, and 16 pin package offer significant advantages in battery life and final product size.
© 1998 MX•COM Inc.
www.mxcom.com Tele: 800 638-5577 336 744-5050 Fax: 336 744-5054
Doc. # 20480136.004
4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA
All trademarks and service marks are held by their respective companies.
CMLMICRO [ CML MICROCIRCUITS ]
