MT88L70
D
EVENTS
A
B
C
E
F
G
t
REC
V
in
t
REC
TONE #n
t
ID
TONE
#n + 1
A
A
A
t
DO
TONE
#n + 1
t
DP
ESt
t
DA
t
GTA
V
TSt
t
GTP
St/GT
t
PQ
t
QStD
Q
1
-Q
4
DECODED TONE # (n-1)
#n
HIGH IMPEDANCE
# (n + 1)
t
PSrD
StD
TOE
t
PTE
t
PTD
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
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.
4-BIT DECODED TONE OUTPUT.
Q
1
-Q
4
StD
TOE
t
REC
t
REC
t
ID
t
DO
t
DP
t
DA
t
GTP
t
GTA
DELAYED STEERING OUTPUT. INDICATES THAT VALID FREQUENCIES HAVE BEEN PRESENT/ABSENT FOR THE
REQUIRED GUARD TIME THUS CONSTITUTING A VALID SIGNAL.
TONE OUTPUT ENABLE (INPUT). A LOW LEVEL SHIFTS Q
1
-Q
4
TO ITS HIGH IMPEDANCE STATE.
MAXIMUM DTMF SIGNAL DURATION NOT DETECTED AS VALID.
MINIMUM DTMF SIGNAL DURATION REQUIRED FOR VALID RECOGNITION.
MINIMUM TIME BETWEEN VALID DTMF SIGNALS.
MAXIMUM ALLOWABLE DROP OUT 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 7 - Timing Diagram
4-31
MITEL [ MITEL NETWORKS CORPORATION ]
