ml7084-001 Oki Semiconductor, ml7084-001 Datasheet - Page 185

• Manufacturer Part Number: ml7084-001
• Description: 4ch Voip Codec
• Manufacturer: Oki Semiconductor

DTMF Detector 0 (DTMFDET0)
This detector can detect the DTMF signal on the transmit side of CH0.
The DTMF detector 0 consists of a DTMF detection section that detects the DTMF signal, a noise detection section
that detects signals other than the DTMF signal, a ON guard timer and a OFF guard timer.
The DTMF detector 0 is enabled when the control register DTMF0_EN is “1”. If it detects a valid DTMF signal (a
DTMF signal is detected and in a state where no noise detected), DTMF0_DET is set to “1”, and the receive code is
stored in DTMF0_C[3:0]. If a DTMF signal is not detected, or DTMF0_EN is “0”, DTMF0_DET will be “0” and
DTMF0_C[3:0] will be “0000.” Figure 51 shows the DTMF detection timing. This detector can adjust the detection
time with the ON and OFF guard timers, and also can adjust the detection level. The initial values of both guard
timers are 20 ms. And the initial value of the detection level is –37.0 dBm0.
A. : DTMF0 enable control register (DTMF0_EN)
B. : DTMF0 detection code indication register (DTMF0_C[3:0])
C. : DTMF0 detection status register (DTMF0_DET)
D. Internal data memory for DTMF0 detection level control (DTMF0_TH)
OKI Semiconductor
0 : Stop (Initial value)
1 : Operate
While the DTMF0 enable control register (DTMF0_EN) is set to “1”, a detected code is stored during the period
where the DTMF is being detected (DTMF0 detection status register DTMF0_DET = “1”).
If the DTMF signal is not detected (DTMF0_DET = “0”), “0000” will be output. (Initial value :0000b)
0 : No DTMF signal detected (Initial value)
1 : DTMF signal detected
Initial value : 1000h (–37.0 dBm0)
Compute the setting value using the following equation when changing the detect level.
Equation: 1000h×1/GAIN
Example: Increasing the detect level by 6 dB.
1000h × 0.5 = 0800h
Upper limit: +12 dB
Lower limit: –12 dB
DTMF detection section
Noise detection section
DTMF code output
DTMF detecting
(DTMF_C[3:0])
internal signal
DTMF0_DET
DTMF0_EN
Input
Figure 51 DTMF Detection Timing
ON guard timer
(data: 0405h)
(data: 3FB2h)
Voice
"0000"
DTMF signal
Detected code
OFF guard timer
"0000"
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