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M-8870
Teltone Corporation, 22121-20th Avenue SE, Bothell, WA 98021-4408 U.S.A
Phone: 800-426-3926 or 425-487-1515 Fax: 425-487-2288
40-406-00011, Rev. E
E-mail: info@teltone.com Internet: www.teltone.com
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 decoded 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
VIN
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.
tREC
Maximum DTMF signal duration not detected as valid.
tREC
Minimum DTMF signal duration required for valid recognition.
tID
Minimum time between valid DTMF signals.
tDO
Maximum allowable dropout during valid DTMF signal.
tDP
Time to detect the presence of valid DTMF signals.
tDA
Time to detect the absence of valid DTMF signals.
TGTP
Guard time, tone present.
TGTA
Guard time, tone absent.
Figure 8 Timing Diagram