V.22 bis Modem with AT Commands
CMX866
©
2008 CML Microsystems Plc
50
D/866/5
DTMF Decoder
Notes
Min.
Typ.
Max.
Unit
Valid input signal levels
(each tone of composite signal)
10
-30.0
-
0.0
dBm
Not decode level
(either tone of composite signal)
10
-
-
-36.0
dBm
Twist = High Tone/Low Tone
-10.0
-
6.0
dB
Frequency Detect Bandwidth
±1.8
-
-
%
Frequency Not Detect Bandwidth
-
-
±3.5
%
Max level of low frequency noise (i.e dial tone)
Interfering signal frequency <= 550Hz
14
-
-
0.0
dB
Interfering signal frequency <= 450Hz
14
-
-
10.0
dB
Interfering signal frequency <= 200Hz
14
-
-
20.0
dB
Max. noise level wrt. signal
14,15
-
-
-10.0
dB
DTMF detect response time
17
-
40.0
-
ms
DTMF de-response time
-
-
30.0
ms
Status Register b5 high time
14.0
-
-
ms
‘Will Detect’ DTMF signal duration
40.0
-
-
ms
‘Will Not Detect’ DTMF signal duration
-
25.0
-
ms
Pause length detected
30.0
-
-
ms
Pause length ignored
-
-
15.0
ms
Notes: 1.
At
25
°
C, not including any current drawn from the CMX866 pins by external circuitry other
than X1, C1 and C2.
2. All logic inputs at V
SS
except for RT, DTRN and RTSN inputs which are at DV
DD
.
3. DSP is powered up but in a reset state.
4. Excluding RD and RT pins.
5. % carrier frequency accuracy is the same as XTAL/CLOCK % frequency accuracy.
6 Tx signal % baud or bit rate accuracy is the same as XTAL/CLOCK % frequency
accuracy.
7. Measured between TXA and TXAN pins with Tx Level Control gain set to 0dB, 1k2
Ω
load
between TXA and TXAN, at V
DD
= 3.0V (levels are proportional to V
DD
- see section
1.4.2). Level measurements for all modem modes are performed with random transmitted
data and without any guard tone. 0dBm = 775mVrms.
8. Measured on the 2 or 4-wire line using the line interface circuits described in section 1.4.2
with the Tx line signal level set to -10dBm for QAM, DPSK, FSK or single tones, -6dBm
and -8dBm for DTMF tones. Excludes any distortion due to external components such as
the line coupling transformer.
9. These are the bit and baud rates of the line signal, the acceptable tolerance is ±0.01%.
10. Rx 2 or 4-wire line signal level assuming 1dB loss in line coupling transformer with Rx
Gain Control block set to 0dB and external components as section 1.4.2.
11. Thresholds and times measured with random data for QAM and DPSK modes,
continuous binary ‘1’ for all FSK modes. Fixed compromise line equaliser enabled.
Signal switched between off and -33dBm
12. ‘Typical’ value refers to 2100Hz or 2225Hz signal switched between off and -33dBm.
Times measured with respect to the received line signal
13. ‘Typical’ values refers to 400Hz signal switched between off and -33dBm
14. Referenced to DTMF tone of lower amplitude.
15. Flat Gaussian Noise in 300-3400Hz band.
16. For V.23r (Tx1200/Rx75) and Bell 202r (Tx1200/Rx150) the calling modem carrier detect
time is typically 1700ms.
17. The decode time is directly affected by signal quality but, for good signals, will always be
much less than the 100ms required for PSTN use.