ISO2-CMOS MT8870D/MT8870D-1
D
A
B
C
E
F
G
EVENTS
tREC
tDO
tID
tREC
TONE
#n + 1
TONE
#n + 1
TONE #n
Vin
tDP
tDA
ESt
tGTA
tGTP
VTSt
St/GT
tPQ
tQStD
HIGH IMPEDANCE
Q1-Q4
# n
# (n + 1)
DECODED TONE # (n-1)
tPSrD
StD
tPTE
tPTD
TOE
EXPLANATION OF EVENTS
A)
B)
C)
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.
D)
E)
OUTPUTS SWITCHED TO HIGH IMPEDANCE STATE.
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
Vin
DTMF COMPOSITE INPUT SIGNAL.
ESt
EARLY STEERING OUTPUT. INDICATES DETECTION OF VALID TONE FREQUENCIES.
STEERING INPUT/GUARD TIME OUTPUT. DRIVES EXTERNAL RC TIMING CIRCUIT.
4-BIT DECODED TONE OUTPUT.
St/GT
Q1-Q4
StD
DELAYED STEERING OUTPUT. INDICATES THAT VALID FREQUENCIES HAVE BEEN PRESENT/ABSENT FOR THE
REQUIRED GUARD TIME THUS CONSTITUTING A VALID SIGNAL.
TOE
tREC
tREC
tID
TONE OUTPUT ENABLE (INPUT). A LOW LEVEL SHIFTS Q1-Q4 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.
tDO
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.
tDP
tDA
tGTP
tGTA
GUARD TIME, TONE ABSENT.
Figure 11 - Timing Diagram
4-21
MITEL [ MITEL NETWORKS CORPORATION ]
