HT8665 datasheet(6/13 Pages) HOLTEK

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Functional Description

The HT8665 is a single chip LSI with an exter-

nal DRAM. It is designed for applications on

talking back with an echo effect. The recording

length of the IC is decided by the data rate

along with the size of an external memory.

Sounds input from an external microphone are

coded through an internal ADM algorithm and

saved in an external memory until the memory

is full or an interval of silence lasts over 0.5

seconds. Once recording is terminated, the IC

will play back the recorded sounds with an echo

effect automatically.

Record function

The HT8665 provides 2 kinds of sampling rate

as well as DRAM interfaces. The sampling rate

(S.R.) along with DRAM determine the record-

ing capacity as shown in the following table: (for

FOSC=640 KHz)

MS (DRAM)

16KB (S.R.)

Recording

Capacity

1 (64Kb)

1 (32K bps)

2 seconds

1 (64Kb)

0 (16K bps)

4 seconds

0 (256Kb)

1 (32K bps)

8 seconds

0 (256Kb)

0 (16K bps)

16 seconds

Notes: “1” is connected to VDD or left open.

“0” is connected to VSS.

Recording starts whenever a sound input is

detected. It then stops once silence is detected

or the recording capacity is full. After that, talk-

ing back comes into play.

Play function

The HT8665 stops to play back the recorded

sounds when an interval of silence lasts 0.5

seconds or the memory is full during recording.

Its playing rate is the same as the rates of

recording and echo effect. The echo delay time

is settable by the DS pin as shown.

DRAM

64Kb

256ms

128ms

256Kb

512ms

256ms

Power control

The HT8665 provides a START pin for power

control. The START pin is of high impedance

and switch Q is turned off at initial. After the

START key is triggered, it will output a high

level signal and switch Q is turned on. This pin

outputs a low level signal and the power of LSI

is switched off when a REC/PLAY cycle has

been implemented 64 times or an interval of

silence lasts over 2 minutes.

Motor

The HT8665 provides a motor driving pin. The

motor is turned on during playing but off once

talking back is terminated.

Status display

The HT8665 provides an LEDB pin to display

its operation status.An external LED is

switched on when the IC is in the standby state.

It, on the other hand, is switched off when the

IC is in the playing state. The LED will flash

with the sound volume when the IC is in the

recording state, but its intensity will vary in-

versely with the volume.

DRAM

Step Size

Estimation

Accumulator

D/A

Delay

VDD

START

VSS

HT8665

21st Dec ’95

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