ISO
2
-CMOS
MT8870D/MT8870D-1
D
EVENTS
t
REC
A
t
REC
B
C
t
ID
E
t
DO
TONE
#n + 1
F
G
V
in
t
DP
ESt
t
GTP
St/GT
t
PQ
TONE #n
AA
AA
AA
AA
TONE
#n + 1
t
DA
t
GTA
V
TSt
t
QStD
Q
1
-Q
4
DECODED TONE # (n-1)
t
PSrD
StD
TOE
#n
HIGH IMPEDANCE
# (n + 1)
t
PTE
t
PTD
EXPLANATION OF EVENTS
A)
B)
C)
D)
E)
F)
G)
TONE BURSTS DETECTED, TONE DURATION INVALID, OUTPUTS NOT UPDATED.
TONE #n DETECTED, TONE DURATION VALID, TONE DECODED AND LATCHED IN OUTPUTS
END OF TONE #n DETECTED, TONE ABSENT DURATION VALID, OUTPUTS REMIAN LATCHED UNTIL NEXT VALID
TONE.
OUTPUTS SWITCHED TO HIGH IMPEDANCE STATE.
TONE #n + 1 DETECTED, TONE DURATION VALID, TONE DECODED AND LATCHED IN OUTPUTS (CURRENTLY
HIGH IMPEDANCE).
ACCEPTABLE DROPOUT OF TONE #n + 1, TONE ABSENT DURATION INVALID, OUTPUTS REMAIN LATCHED.
END OF TONE #n + 1 DETECTED, TONE ABSENT DURATION VALID, OUTPUTS REMAIN LATCHED UNTIL NEXT
VALID TONE.
EXPLANATION OF SYMBOLS
V
in
ESt
St/GT
Q
1
-Q
4
StD
TOE
t
REC
t
REC
t
ID
t
DO
t
DP
t
DA
t
GTP
t
GTA
DTMF COMPOSITE INPUT SIGNAL.
EARLY STEERING OUTPUT. INDICATES DETECTION OF VALID TONE FREQUENCIES.
STEERING INPUT/GUARD TIME OUTPUT. DRIVES EXTERNAL RC TIMING CIRCUIT.
4-BIT DECODED TONE OUTPUT.
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 DETECED AS VALID
MINIMUM DTMF SIGNAL DURATION REQUIRED FOR VALID RECOGNITION
MAXIMUM 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 11 - Timing Diagram
4-21
MITEL [ MITEL NETWORKS CORPORATION ]
