SM8223A Datasheet, PDF (13/15 Pages) Nippon Precision Circuits Inc – FSK Decoder and DTMF Receiver IC

SM8223A
DTMF signal
DTMF DATA
DOUT
0 Q0 Q1 Q2 Q3 S0 S1 S2 S3 1
Start bit
DTMF data
(LSB first)
Checksum
(2'mod16)
Stop bit
(LSB first)
Figure 5. DTMF signal to DOUT output
The DTMF receiver determines whether the received
data (DTMF signal) is valid after an interval of
t_REC ≥ 40ms stable reception. If valid, DV goes
LOW and data is output on DOUT. If DTMF data is
not detected after an interval t_SPA ≥ 20ms, a data
pause is activated and the next DTMF signal is in a
wait state (see timing diagrams in AC Electrical
Characteristics). The SM8223A DTMF receiver can
be used as a general-purpose DTMF receiver without
the need for the external time constant circuit, in
which case the resistor/capacitor/diode network can
be omitted.
NIPPON PRECISION CIRCUITS—13