MT88L70 Zarlink Semiconductor, MT88L70 Datasheet - Page 9

• Manufacturer Part Number: MT88L70
• Description: 3 Volt Integrated DTMF Receiver
• Manufacturer: Zarlink Semiconductor

EXPLANATION OF EVENTS
A)
B)
C)
D)
E)
F)
G)
EXPLANATION OF SYMBOLS
V
ESt
St/GT
Q
StD
TOE
t
t
t
t
t
t
t
t
REC
REC
ID
DO
DP
DA
GTP
GTA
V
ESt
St/GT
Q
StD
TOE
in
1
in
-Q
EVENTS
1
-Q
4
4
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 REMAIN 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.
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
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.
t
REC
A
DECODED TONE # (n-1)
t
DP
t
GTP
t
PSrD
t
PQ
Figure 7 - Timing Diagram
t
REC
TONE #n
B
t
QStD
C
# n
1
t
-Q
ID
t
4
DA
TO ITS HIGH IMPEDANCE STATE.
t
GTA
#n + 1
TONE
E
HIGH IMPEDANCE
t
PTD
t
DO
D
F
TONE
#n + 1
# (n + 1)
t
PTE
G
MT88L70
V
TSt
4-31