Calling Line Identifier
FX602
A.
B.
C.
D.
E.
F.
Normal conversation with both near and far end voice present.
Central Office mutes far end voice, sends CAS and becomes silent.
CPE recognises CIDCW initiation and mutes near end voice and keypad.
CPE sends dtmf ACK to Central Office to signal its readiness to receive FSK data.
Central Office recognises ACK and sends FSK Caller ID data to CPE.
CIDCW transaction is complete. CPE unmutes near end voice and the Central Office
unmutes far end voice, returning to normal conversation.
Figure 9a : CIDCW Transaction from Near End CPE Perspective
From the near end CPE’s perspective, the initiation of a CIDCW transaction is characterized by two events
occurring in sequence: (1) a CAS dual tone burst is received, and (2) a subsequent quiet period passes as far
end speech continues to be muted. In the algorithm to be described these two events are detected by the
FX602’s Dual Tone Alert detector and FSK level detector, respectively.
Caller ID and CIDCW products require a microcontroller to manage the transfer and display of Caller ID data.
The same microcontroller is easily used to observe and control the FX602 CIDCW transaction initiation
detection process. This involves measuring the FX602 DET output pulse duration, controlling the muting of
near end voice, watching for further DET output activity, and controlling whether the FX602 is in Dual Tone
Alert or FSK Receive modes, as shown in Figure 9b below.
Figure 9b : FX602 Operation during CIDCW Transaction
ã 1998 Consumer Microcircuits Limited
16
D/602/7
CMLMICRO [ CML MICROCIRCUITS ]
