AT76C101

2

Description

The AT76C101 is an Image Compression/Decompression

Processor that performs the JPEG Baseline Algorithm. The

system is capable of high quality compression and decom-

pression of continues-tone color or monochrome images.

The AT76C101 performs the Discrete Cosine Transform,

Quantization, and Entropy Encoding during the compres-

sion stage and carries out all inverse operations during the

decompression phase. The AT76C101 uses an external

SRAM as working memory, which is accessed by an on-

chip video interface.

The AT76C101 is designed to operate with minimum host

intervention. A host processor is required to program the

chip in the required operating mode, and to extract the

JPEG header from the compressed bit stream during the

decompression phase. Based on this information, it then

initializes the internal registers. Once the chip has been ini-

tialized, the AT76C101 operates continuously until it has

completed compression/decompression of a image frame.

The image compression ratio is controlled by the user sup-

plied quantization tables, which are loaded before the com-

pression/decompression operation. Compression ratios

from 1:1 to 50:1 are possible depending on the quality and

storage requirements of the application.

Basic System Configuration

An AT76C101-based image compression system is shown

in Figure 1. The AT76C101 requires the following external

devices:

• A microcontroller to program and initialize the chip in the

required operating mode. This device is also used to

strip the JPEG header during decompression and to

provide the AT76C101 with the header information.

• An external working memory (SRAM) for handling

uncompressed/decompressed images. The size of this

memory depends on the size of the image being

processed. The formula to assess the memory size is

given in the Pixel Interface section of this manual.

• An external memory device to store the compressed

data stream. This external memory can be either a fast

memory or a slow inexpensive memory. The size of this

memory

depends

on

the

needs

of

the

specific

application.

Figure 1. AT76C101-based Image Compression System

RAW_OUT

SAMPLING & COLOR

CONVERSION

PXWE

PXRE

PXIN

PXOUT

STOP_PIXEL

SRDRIVE

H_SYNC

V_SYNC

PX_CLK

CLK_IN

MEM_CS

TEST

RESET

FRAMEND

FREEZE

MASTER_CS

MASTER_WR

MASTER_OE

BUSY

32K x 16

SRAM

DATA15-0

ADDR15-0

RE

WE

YUV

RGB

IMAGE TO

DISPLAY

Image

Source

24-BIT

RGB

COMPRESSED

DATA

MEMORY

ADDR19-0

DATA7-0

CS

WR

OE

MICROCONTROLLER

AT76C101