Calling Line Identifier with VMWI
CMX612
hook applications, the longer (88 to 110ms) Tone Alert signal employed by BT for on-hook applications
will not necessarily cause IRQN to go low.
See Section 1.7.1 for definitions of Tton, Ttoff and TqCAS
Figure 6 : Tone Alert Detector operation
1.5.8 Dial Tone Detector
This block is enabled when the CMX612 is set to Dial Tone Detect mode. It will then monitor the received
signal for the presence of simultaneous 350Hz and 440Hz tones of sufficient level and duration.
Two digital bandpass filters, centred around 350Hz and 440Hz, are used within the block to give
additional rejection of interfering signals. The CMX612 DET output will be set high while a Dial Tone
signal is detected. At the end of the Dial Tone signal the detector will derespond in 24ms typically. Since
the deresponse time is governed by a statistical process, there will be occasions when the maximum
figure of 33ms is exceeded.
When the DET output goes high the IRQN output will be pulled low and will remain low until the CMX612
is switched out of Dial Tone Detect mode. Note that the Dial Tone Detect timing has been optimised for
the detection of >90ms signals. Shorter dial tone signals will not necessarily be detected.
See Section 1.7.1 for definitions of Tdon and Tdoff
Figure 7 : Dial Tone Detector operation
ã 2002 Consumer Microcircuits Limited
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D/612/3
CMLMICRO [ CML MICROCIRCUITS ]
