MT8870 Mitel Networks Corporation, MT8870 Datasheet - Page 11

• Manufacturer Part Number: MT8870
• Description: ISO2-CMOS Integrated DTMF Receiver
• Manufacturer: Mitel Networks Corporation

A)
B)
C)
D)
E)
F)
G)
V
ESt
St/GT
Q
StD
TOE
t
t
t
t
t
t
t
t
EXPLANATION OF EVENTS
EXPLANATION OF SYMBOLS
REC
REC
ID
DO
DP
DA
GTP
GTA
in
V
ESt
St/GT
Q
StD
TOE
1
-Q
in
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 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.
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 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.
t
REC
A
DECODED TONE # (n-1)
t
DP
t
GTP
t
Figure 11 - Timing Diagram
PSrD
t
PQ
t
REC
TONE #n
B
ISO
2
t
AA
AA
AA
AA AA
AA AA
QStD
-CMOS
C
1
# n
-Q
t
ID
4
t
TO ITS HIGH IMPEDANCE STATE.
DA
t
GTA
TONE
#n + 1
E
HIGH IMPEDANCE
MT8870D/MT8870D-1
t
PTD
t
DO
D
F
TONE
#n + 1
# (n + 1)
t
PTE
G
V
TSt
4-21