MT8870D/MT8870D-1 Data Sheet
16
Zarlink Semiconductor Inc.
Figure 11 - Timing Diagram
EXPLANATION OF EVENTS
EXPLANATION OF SYMBOLS
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 REMIAN 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.
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 DETECED AS VALID
t
REC
MINIMUM DTMF SIGNAL DURATION REQUIRED FOR VALID RECOGNITION
t
ID
MAXIMUM 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.
V
in
ESt
St/GT
Q
1
-Q
4
StD
TOE
EVENTS
ABC
D
EFG
t
REC
t
REC
t
ID
t
DO
TONE #n
TONE
#n + 1
TONE
#n + 1
t
DP
t
DA
t
GTP
t
GTA
t
PQ
t
QStD
t
PSrD
t
PTD
t
PTE
# n
# (n + 1)
HIGH IMPEDANCE
DECODED TONE # (n-1)
V
TSt
