W925EP01 Datasheet, PDF (87/108 Pages) Winbond – 8-BIT CID MICROCONTROLLER

W925EP01/ W925EP01FG
Vin (Tip/ring)
ESt _*
DTMFD
DTMFDF
TONE #n
t DP
t GP
t REC
+
t DA
t GA
t ABS
DTMFDR _{Tone #n-1}
13
Tone #n
23
1: Guard time timer is reset and starts to up count from 00H.
2: Guard time timer is reset and starts to up count from 00H.
3: The content of the up counting timer reaches the register DTMFPT/DTMFAT.
* ESt is an internal signal in the circuit.
+ Clear by software.
Figure 6-17 The Waveform of DTMF Detection
Tone Detector
In off-hook state, said type II system, detecting tone alert signal (CAS) is easily interfered by human’s
voice or other noise in voice band. Sometimes the interference makes falsely recognizing a noise as a
CAS (talk-off), or lost detecting a real CAS (talk-down). The DTMF can be programmed as a tone
detector by setting bit 4 of DTMFR2. The frequency band of the tone detector is DTMF frequency from
697Hz to 1633Hz. Once the tone detector gets signals in the band, the bit of DTMFH or DTMFL in
register DTMFDR will become high immediately. User can poll these 2 bits to check if the tone exists
on the tip/ring. The input gain of tone detector is the same as DTMF receiver.
FSK Decoder
The FSK carrier detector provides an indication of the present of a signal within the FSK frequency
band. If the output amplitude of the FSK band-pass filter is sufficient to be detected continuously for 8
mS, the FSK carrier detected bit FCD will go high and it will be released if the FSK band-pass filter
output amplitude is not able to be detected for greater than 8 mS. The 8 mS is the hysteresis of the
FSK carrier detector. Figure 6-18 shows the timing of FSK carrier detection.
Tip/Ring
FSKE
FCD
t _FSKE ^{Analog FSK Signal}
Note
t _CA
t _CP
Analog FSK Signal
t _CP
t _CA
Figure 6-18 FSK Detection Enable and FSK Carrier Present and Absent Timing
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Publication Release Date: Apr. 10, 2006
Revision A2