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EM78910AAH

8-BIT MICRO-CONTROLLER

ELAN Microelectronics 

EM78910/910A

8-bit Micro-controller

The value of R1 and C1 must be chosen to hold the /RING TIME pin voltage below the Vt+ of the

Schmitt between the individual cycle of the power ring. With /RINGTIME enabled, this signal will be a /RD

signal in RA through a buffer.

VDD

R1

/RINGTIME

C1

/RD

R2

RDET1

R3

Fig.14 ring detect circuit

VII.10 DTMF ( Dual Tone Multi Frequency ) Tone Generator

Built-in DTMF generator can generate dialing tone signals for telephone of dialing tone type. There are

two kinds of DTMF tone. One is the group of row frequency, the other is the group of column frequency, each

group has 4 kinds of frequency, and user can get 16 kinds of DTMF frequency totally. DTMF generator contains

a row frequency sine wave generator for generating the DTMF signal, which selected by low order 4 bits of RB

and a column frequency sine wave generator for generating the DTMF signal, which selected by high order 4 bits

of RB. This block can generate single tone by filling one bit zero to this register.

If all the values are high, the power of DTMF will turn off until one or two low values.

Either high or low 4 bits must be set by an effective value, otherwise, if any ineffective value or both 4

bits are load effective value, tone output will be disable. Recommend value refer to table as follow please :

Row-register bits

SYSTEM CLOCK

Row-frequency generator

DTMF row(low)-freq.

selection

Sine wave

generator

DTMF column(high)-freq.

selection

Sine wave

generator

Column-register bits

Column-frequency generator

Fig.15 DTMF Block Diagram

TONE

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* This specification are subject to be changed without notice.

~ 21~

2001/01/12

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