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D6571E

EASYTAD™ Chip for an All- Digital Telephone Answering Machine with Flash Memory Interface

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D6571E Data Sheet

FUNCTIONAL DESCRIPTION

HOST Interface

The HOST interface is an 8-bit parallel data port, used

for control and status information transfer. The HOST

controls the operation of the D6571E using a simple

command protocol. D6571E status information is

updated after each command.

The command and status protocol enables the HOST to

have full control over the functions of the D6571E. This

protocol is described in details in the following sections.

Voice Message Recording Incoming and Outgoing

Messages

The D6571E message storage utilizes a proprietary, high

quality speech compression algorithm to reduce the

data rate of the speech signal. The compression

algorithm is programmable and can support different bit

rates: high, middle, and low bit rate. Each of the rates

can be activated with “gap coding.” When activated

with no “gap coding” the D6571E provides 9.6, 7.2, and

4.4 Kbps respectively at 8 Khz sampling rate. At 7.2 Khz

sampling rate bit rate will be 10% lower. When the

compression algorithm utilizes both low bit rate and

“gap coding”, the D6571E achieves a recording time of

22-25 minutes in a 4 Mbit device using a 8000 Hz

sampling rate. At 7200 Hz sampling rate the D6571E

provides 24 - 27 min of recording time. The chip can

support up to four 4 Mbit devices or one 16 Mbit device.

The chipset supports up to 128 variable length incoming

and outgoing messages. Multiple outgoing messages

and multiple mailboxes for incoming messages are

supported.

During recording, the D6571E performs telephone line

signal monitoring. The HOST can stop recording and

delete unwanted information (silence or telephone

signaling) by performing a “Tail Cut”. The Host can

delete the last n*TCF seconds from the memory using a

Record command with a Tail Cut Factor (TCF). Tail Cut

Factor is 0.160 seconds for 8 KHz sampling rate and

0.176 seconds for 7.2 KHz. For PCM messages Tail Cut

increment is 240 ms or 266 ms respectively.

A message with less than 1 second duration won’t be

stored in the message directory.

During record mode the HOST can instruct the D6571E

to generate an audible tone to the telephone line. The

recorded audio signal that is digitized through the

CODEC input is transmitted back through the CODEC

output for call screening and other features. This Loop-

Back function can be disabled by the HOST in the

Record command.

Digital Voice-Activated Recording (VOX)

Digital voice activity detection is implemented in the

D6571E and can be activated only in Record mode.

According to the HOST command recording of the

speech signal may either start upon a positive result of

voice activity detection or immediately after issuing a

Record command.

The voice activity detector output is reported to the

HOST via a status bit every frame when in Record mode.

The HOST reads this information and decides when to

stop recording of the message.

Automatic Gain Control

The D6571E supports AGC in Record mode. AGC can

be enabled/disabled by the Host. Parameters of the

AGC are Host programmable.

Message Playback

The D6571E supports random access for playback of

any recorded message. During playback, the D6571E

monitors the telephone line.

Offset and FLEXISPEECH™

Each message can be played from the beginning of the

message or from any given offset point along the

message (in 0.64 second increments). The HOST can

also read during playback, the current offset position in

order to implement jumps within the message. For PCM

messages offset increment is 0.93 sec for 8 KHz

sampling rate (1.03 sec for 7.2 KHz sampling rate). The

D6571E also supports FLEXISPEECH™ , variable speed

playback, with a range of 0.5 to 2.0 relative to the

original speed. The FLEXISPEECH™ feature allows

listening to messages at different speeds without

changing the voice characteristics and without

degradation of the voice quality.

Message playback can be stopped by using the Pause

command, which is initiated by the HOST. After Pause,

DS6571E.2

DSP GROUP, INC., 3120 SCOTT BOULEVARD

9

SANTA CLARA, CA 95054 PH: 408 986-4300 FAX: 408 986-4490

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