Dual-Tone Detection; Off-Hook Detection - Epson S1C05251 Technical Manual

3 FUNCTIONAL DESCRIPTION

3.6 Dual-Tone Detection

Dual tones (Bellcore CPE alert signal (CAS), British Telecom tone alert signal) are detected using two tone filters
and digital identification circuits. If dual tones are received when the PDWN pin is set low and CAS mode has been
selected by the host CPU, the #DET pin and the #IRQ pin changes to Low level.
Parameter
Low tone frequency
High tone frequency
Receive signal level
Rejection signal level
Receive tone twist
Tone output time
Simultaneous voice
reception

3.7 Off-Hook Detection

Figure 3.7.1 shows an example of an off-hook detection circuit. Set the MODE1 pin to 1 to detect off-hook status.
The example below can detect on-hook/off-hook status even if the device is in the power down mode. The hook
status is detected by comparing the voltage values between the HOOK and EXTREF pins. When off-hook (HOOK
pin voltage < EXTREF pin voltage) is detected, the #RDET pin outputs 0.
TIP
RING
16
Table 3.6.1 Dual-tone characteristics
Bellcore
(CPE alert signal)
2130 Hz ±0.5%
2750 Hz ±0.5%
-32 dBm to -14 dBm/tone,
off-hook
≤ -45 dBm
0 to 6 dB
75 msec to 85 msec
Yes
HOOK
EXTREF
Figure 3.7.1 Off-hook detection circuit
EPSON
BT (tone alert signal)
Line disconnected
2130 Hz ±1.1%
2750 Hz ±1.1%
-40 dBV to -2 dBV/tone,
on-hook
≤ -46 dBV
0 to 7 dB
88 msec to 110 msec
No
RING
–
Amp( )
MODE1 = 1
+
Line connected
2130 Hz ±0.6%
2750 Hz ±0.6%
-40 dBV to -8 dBV/tone,
off-hook
0 to 7 dB
80 msec to 85 msec
Yes
#RDET
S1C05251 TECHNICAL MANUAL