M-88L70 Datasheet, PDF (6/8 Pages) Clare, Inc. – 3V DTMF Receiver

M-88L70
Figure 4 Single-Ended Input Configuration
Figure 5 Guard Time Adjustment
Figure 6 Timing Diagram
Explanation of Events
(A) Tone bursts detected, tone duration invalid, outputs not
updated.
(B) Tone #n detected, tone duration valid, tone decoded
and latched in outputs.
(C) End of tone #n detected, tone absent duration valid,
outputs remain latched until next valid tone.
(D) Outputs switched to high impedance state.
(E) Tone #n + 1 detected, tone duration valid, tone decod-
ed and latched in outputs (currently high impedance).
(F) Acceptable dropout of tone #n + 1, tone absent duration
invalid, outputs remain latched.
(G) End of tone #n + 1 detected, tone absent duration valid,
outputs remain latched until next valid tone.
Explanation of Symbols
V_IN
DTMF composite input signal.
ESt
Early steering output. Indicates detection of
valid tone frequencies.
St/GT
Steering input/guard time output. Drives
external RC timing circuit.
Q1 - Q4 4-bit decoded tone output.
StD
Delayed steering output. Indicates that valid
frequencies have been present/absent for
the required guard time, thus constituting a
valid signal.
OE
Output enable (input). A low level shifts Q1 -
Q4 to its high impedance state.
t_REC
Maximum DTMF signal duration not detected
as valid.
t_REC
Minimum DTMF signal duration required for
valid recognition.
t_ID
Minimum time between valid DTMF signals.
t_DO
Maximum allowable dropout during valid DTMF
signal.
t_DP
Time to detect the presence of valid DTMF
signals.
t_DA
Time to detect the absence of valid DTMF
signals.
t_GTP
Guard time, tone present.
t_GTA
Guard time, tone absent.
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