BU8872 データシートの表示（PDF） - ROHM Semiconductor

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BU8872

DTMF receiver for telephones

ROHM Semiconductor 

Communication ICs

(3) DTMF input

BU8872 / BU8872FS

The relation between a momentary falter in the ESt guard

time (tGL), a momentary HIGH level in the ESt guard time

(tGH), and the time constant is shown below. Figure 10

shows a timing diagram for guard times.

C501 : This is the DC blocking capacitor. Select a ca-

pacitor that will pass DTMF signals (greater

than 697Hz) without significantly attenuating

the signals.

JP592 : If DTMF signals are being input directly, both

ends should be shorted.

C591

R591 X R595 Use these to increase the sensitivity of

C592, C593 the DTMF receiver.

(4) ESt output

The ESt guard time is determined by the CPU of the host

computer, but to reduce the load on the host computer,

the guard time can be set using an external circuit, as

shown below.

199

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