FEDL7020-02

1Semiconductor

ML7020

10/19

Figure 3

DTMF reception timing

t

Input signal persistence duration (detection)

Normal reception is made when the input signal persistence duration is equal to t

t

Input signal persistence duration (non-detection)

The input signal is ignored when the input signal persistence duration is less than t

receive data are not output.

t

Signal quiet duration

The DTMF receive data and SP are reset if the input continues to be in the no-signal condition for a

duration equal to t

Also, even if the receive data changes during DTMF signal reception, SP continues to be “1” and the

DTMF receive data may remain in the initial value and may not change, if the signal quiet duration is less

than t

t

Instantaneous break protection period 1

This is applicable to the period after the input signal has arrived and until the timing when SP becomes “1”.

In other words, SP and DTMF receive data are output normally even if a no-signal condition of a duration

less than t

t

Instantaneous break protection period 2

This is applicable when SP is “1” (during output of the receive data).

In other words, SP and the DTMF

receive data are not reset even if a no-signal condition of a duration less than t

reception.

t

For ensuring normal reception, make sure that the signal repetition period is equal to t

t

Detection delay time

The DTMF receive data is output with a delay of t

t

Detection hold time

The output of SP or the DTMF receive data is stopped with a delay of t

signal.

t

SP delay time

SP is output after a delay of t

Therefore, latch the

DTMF receive data when the rising edge of SP is detected.

t

s

t

p

t

c

t

bb

t

d

t

g

DTMF signal

DTMF receive data

SP

t

l

t

sp

t

ba