MT88L70
D
EVENTS
A
B
C
E
F
G
Data Sheet
t
REC
V
in
t
REC
TONE #n
t
ID
TONE
#n + 1
t
DO
TONE
#n + 1
t
DP
ESt
t
DA
t
GTP
t
GTA
V
TSt
t
PQ
St/GT
t
QStD
#n
Q
1
-Q
4
DECODED TONE # (n-1)
HIGH IMPEDANCE
# (n + 1)
t
PSrD
StD
TOE
t
PTD
t
PTE
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.
Q
1
-Q
4
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.
TOE
TONE OUTPUT ENABLE (INPUT). A LOW LEVEL SHIFTS Q
1
-Q
4
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 DROP OUT 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.
Figure 7 - Timing Diagram
12
Zarlink Semiconductor Inc.
ZARLINK [ ZARLINK SEMICONDUCTOR INC ]
