MT8870D/MT8870D-1

4-21

Figure 11 - Timing Diagram

ESt

St/GT

StD

TOE

EVENTS

AB

C

D

EF

G

TONE #n

TONE

#n + 1

TONE

#n + 1

# n

# (n + 1)

HIGH IMPEDANCE

DECODED TONE # (n-1)

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.

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.

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

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.