HT95R64 datasheet(56/82 Pages) HOLTEK

56 / 82 page

HT95R64/HT95R65

Rev. 1.00

March 3, 2010

DTMF Receiver

The device contains a fully integrated DTMF receiver which will decode the DTMF frequency content of incoming ana-

log DTMF signals. An internal operational amplifier is also supplied to adjust the input signal level as shown. There is

also a pre-filter function which is a band rejection filter tp reject frequencies between 350Hz and 400Hz. The low group

filter filters the low group frequency signal output, whereas the high group filter filters the high group frequency signal

output. Each filter output is followed by a zero-crossing detector which includes hysteresis. When the signal amplitude

at the output exceeds a specified level, it is transferred into a full swing logic signal.

When the input signal is recognized as an effective DTMF tone, a peripheral interrupt will be generated, and the corre-

sponding DTMF tone code will be generated.

Bit No.

Label

R/W

Function

R_PWDN

DTMF Receiver Power Down Enable

R_PWDN= 0

® The DTMF receiver is in normal mode;

R_PWDN= 1

® The DTMF receiver is in power down mode

After reset, R_PWDN = 1

R_INH

Inhibit the detection of tones representing characters A, B, C and D

R_INH= 0

® detect tones representing characters A, B, C and D

R_INH= 1

® ignore tones representing characters A, B, C and D

After reset, R_INH = 0

R_DV

Data valid output flag

R_DV= 0

® There is no valid DTMF tone received

R_DV= 1

® There is a valid DTMF tone received

7~3

Unused bit, read as

²0²

Note: R_DV should be cleared manually if necessary.

DTMF Receiver Status

( a ) S t a n d a r d I n p u t C i r c u i t

V N

G S

V R E F

R 1

R F

V P

V i

V N

G S

V R E F

C 2

R 2

R 5

( b ) D i f f e r e n t i a l I n p u t C i r c u i t

V P

R 4

R 3

C 1

R 1

V i 1

V i 2

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