
D6571E Data Sheet
DS6571E.2
DSP GROUP, INC., 3120 SCOTT BOULEVARD
SANTA CLARA, CA 95054 PH: 408 986-4300 FAX: 408 986-4490
90
In this mode, the D6571E receives linear PCM data via
Host Data Bus in burst of 240 words, compresses it with
TRUESPEECH compression algorithm, and transmits it
back via Host Data Bus in bursts of bytes. The size of
bursts depends on the compression rate.
The TRUESPEECH compression algorithm implemented
in the D6571E is Host programmable and is able to utilize
three compression rates as well as “gap coding”. The
first Voice Data Compression command C1 defines the
compression rate.
Then the Host issues command C2. This command
contains the number of words the Host is going to
transmit to the D6571E. The D6571E returns status S2,
which contains the number of words the D6571E will
accept from the Host. Upon receiving S2 the actual
Word Transfer begins. The Host sends 240 words of
uncompressed speech data. The D6571E responds with
an echo of each word.
Upon receiving uncompressed speech the D6571E starts
compression of the current frame. The Host issues the
C3 command, which will be accepted by the D6571E
after compression of the current frame is accepted. The
C3 command contains the number of bytes which the
Host expects to receive from the D6571E (48 bytes). In
the status S3, the D6571E informs the Host the actual
number of bytes the D6571E will transmit.
After Host reads the status S3, the actual Byte Transfer
begins. The Host uses the high byte (bits 15-8) of the
Data Transfer Command. In response to a command the
D6571E sends the byte of compressed data in the high
byte (bits 15-8) of the Data Transfer status.
With Byte Transfer, the HI/LO pin (pin 4) of the D6571E
should be set to high during the command/status
sequence. The Host can still send a word to the D6571E,
but the low byte will be ignored by the D6571E during
Byte Transfer.
The Host sends the Next C1 command to start
processing the next frame. In this manner, the D6571E
compresses and transmits data frame by frame. This
mode can be terminated by issuing an Idle command
instead of command C2. In addition, at each command
(C1, C2 and C3) the D6571E checks bits 15-12 for the
correct code. If an incorrect code is detected, the
D6571E will return to Idle mode.
The performance of the mode is the same in case of
“cold start.”
Data Decompression Mode
In this mode, the D6571E receives speech data
previously compressed with TRUESPEECH via the Host
Data Bus, compresses it, and transmits it back in linear
format in bursts of words.
The D6571E receives the first Data Decompression
command C1 and returns status S1. Then the Host
sends command C2 with the number of bytes that the
Host is going to transmit to the D6571E (48 bytes). The
D6571E returns status S2 with the actual number of
bytes that the D6571E will accept from the Host in the
current frame. After the Host receives S2, the actual
Byte Transfer begins. The Host sends the appropriate
number of Data Transfer commands, which contain
compressed speech and receives an echo of each
command in the Data Transfer status.
The Host sends the byte of data in high byte of the
Data Transfer Command. In response to each command
the D6571E sends back the echo of the byte in the high
byte of the Data Transfer status.
With Byte Transfer, the HI/LO pin (pin 4) of the D6571E
should be set to high during the command/status
sequence.
After the D6571E accepts the bursts of bytes, it starts
decompression. To receive the decompressed data, the
Host sends a C3 command. The C3 command will be
accepted by the D6571E after decompression of the
current frame is completed. Command C3 contains the
number of words the Host expects to receive from the
D6571E (240 words). In status S3, the D6571E sends the
actual number of words the D6571E is going to transmit
to the Host. After the Host receives S3, the Word
Transfer begins. Then the Host sends the appropriate
number of Data Transfer commands and receives a word
of linear PCM data in response to each command (Data
Transfer status).
The Host sends the next C1 command to start
processing the next frame. In this manner, the D6571E
decompresses and transmits data frame by frame. This
mode can be terminated by issuing an Idle command
instead of command C2. In addition, at each command
(C1, C2 and C3) the D6571E checks bits 15-12 for the
correct code. If an incorrect code is detected, the
D6571E will return to Idle mode.