M-8880 Datasheet, PDF (11/13 Pages) Clare, Inc. – M-8880 DTMF Transceiver

M-8880
Explanation of Events
(A) Tone bursts detected, tone duration invalid, RX Data Register not updated.
(B) Tone #n detected, tone duration valid, tone decoded and latched in RX Data Register.
(C) End of tone #n detected, tone absent duration valid, RX Data Register remain latched until next valid tone.
(D) Tone #n + 1 detected, tone duration valid, tone decoded and latched in RX Data Register.
(E) Acceptable dropout of tone #n + 1, tone absent duration invalid, RX Data Register remain latched.
(F) End of tone #n + 1 detected, tone absent duration valid, RX Data Register remain latched until next valid tone.
Explanation of Symbols
V_IN
ESt
St/GT
DTMF composite input signal.
Early steering output. Indicates detection of valid tone frequencies.
Steering input/guard time output. Drives external RC timing circuit.
RX₀-RX₃
b3
b2
4-bit decoded data in receive data register.
Delayed steering output. Indicates that valid frequencies have been present/absent for the
required guard time, thus constituting a valid DTMF signal.
Output enable (input). A low level shifts Q1 - Q4 to its high impedance state.
IRQ/CP
t_REC
t_REC
t_ID
t_DO
t_DP
t_DA
T_GTP
t_GTA
Interrupt is active indicating that new data is in the RX data register. The interrupt is cleared
after the status register is ready.
Maximum DTMF signal duration not detected as valid.
Minimum DTMF signal duration required for valid recognition.
Minimum time between valid DTMF signals.
Maximum allowable dropout during valid DTMF signal.
Time to detect the presence of valid DTMF signals.
Time to detect the absence of valid DTMF signals.
Guard time, tone present.
Guard time, tone absent.
Figure 13 Timing Diagrams
40-406-00012, Rev. G
Page 11
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