SGS Thomson Microelectronics STV0676 Datasheet
®
STV0676
CMOS Digital Camera Co-processor
The STV0676 co-processor combined with ST
CMOS image sensors offers highly integrated
imaging products which deliver USB 1.1, RGBpreview, YCrCb or M-JPEG digital video data at up
to 30 frames per second.
The STV0676 interfaces to CIF (352 x 288) or VGA
(640 x 480) image sensor and performs:
- pixel defect correction,
- auto exposure, auto gain,
- auto white balance, anti-aliasing, anti-flicker,
- colour interpolation, colour balance,
- gamma correction,
- M-JPEG compression.
STV0676 chipsets are supported by a fully- featured
USB driver. This provides a wide range of user
definable settings for optimum camera setup and
operation. Isochronous data transfer over USB
guarantees video quality at all times, irrespective of
the number of other peripherals.
Low power consumption, highly integrated designs
and simple support circuitry enable OEMs to design
low cost, low power, camera products for high
volume consumer market places.
KEY FEATURES
■ Real-time video - up to 30fps VGA
■ USB 1.1 compliant
■ Motion-JPEG compression
■ Isochronous USB data transfer
■ Direct Show driver support
■ Programmable vendor ID
■ RGB-preview, YCrCb or M-JPEG video output
■ Automatic exposure, gain and wh ite balance
APPLICATIONS
USB camera:
- Biometric identification, toys and games
Embedded applications support:
- PDA, notebook PC, mobile phone
- Set top box, and security applications
STMicroelectronics offers camera manufacturers
rapid-to-market camera products supported by
comprehensive reference designs, software drivers
and technical backup.
Typical application
lens + IR filter
October 2002 ADCS 7280926C 1/21
CMOS Sensor
CIF or VGA
image
array
Video
Processor
STV0676
Video
Compression
MIcro
Processor
USB
Interface
USB Cable
to host PC
EEPROM
STV0676
Table of contents
Chapter 1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
1.1 STV0676 co-processor general description .........................................................................5
1.2 Video processor (VP) ...........................................................................................................5
1.2.1 Sensor interface ...................................................................................................5
1.2.2 Video processor functions ....................................................................................6
1.3 Auto exposure and gain control ...........................................................................................7
1.4 Defect correction ..................................................................................................................7
1.5 Video compression (VC) engine ..........................................................................................7
1.6 Control processor .................................................................................................................7
1.7 Power management .............................................................................................................7
Chapter 2 External interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
2.1 USB interface ................................................................ ........... ........... .................................8
2.2 Mode selection .....................................................................................................................9
2.3 Selecting VID and PID via the digiport .................................................................................9
2.4 Serial EEPROM .................................................................................................................10
2.4.1 EEPROM format and contents ...........................................................................11
2.4.2 Strings ................................................................................................................11
2.4.3 CheckSum .........................................................................................................12
2.5 I2C slave mode ..................................................................................................................12
2.6 Digiport ............................................................................................................................... 12
2.7 General purpose input and output ......................................................................................12
Chapter 3 STV0676 application example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13
3.1 USB webcam ...................................................................................... ........... ........... .........13
3.2 Embedded camera .............................................................................................................13
Chapter 4 Detailed specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14
4.1 STV0676 absolute maximum ratings .................................................................................14
4.2 STV0676 AC/DC characteristic ..........................................................................................14
Chapter 5 Pinout and pin descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15
5.1 STV0676 pin details ...........................................................................................................15
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STV0676
Chapter 6 Package Details STV0676 64pin TQFP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19
Chapter 7 Reference design and evaluation kits (RDK’s and EVK’s) . . . . . . . . . . . . . . . .20
Chapter 8 Ordering details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20
Chapter 9 Design issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20
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Document revision history
Table 1 : Document revision history
Revision Date Comments
1.0 17/01/01 First Product preview release
1.1 22/01/01 Information added on
- Microport
- Serial EEPROM
- digiport
2
- Slave I
- I
1.2 01/02/01 Micropor t description up dated
A 07/03/01 Details of existing STV0672 register map removed
Added reference to VV6411 sensor
B 10/10/01 Document reformatted with ST template
C implementation
2
C Register map
STV0676
C 13/08/02 Change from a chipset datasheet to co-processor only.
Update of driver reference and orderi ng details.
4/21 Revision C
STV0676 Overview
1 Overview
1.1 STV0676 co-processor general description
The STV0676 is a digital video processor requiring no external RAM and a minimum of passive
support components to provide a complete USB camera. STV0676 accepts raw digital video data
from a ST VGA or CIF format CMOS sensor and is capab le of tr ansfer ring the resulting JPEG data
to a host PC over USB at rates up to 30 frames per second VGA.
The internal STV0676 architecture consists of a number of separate functional blocks:
● Video processor (VP)
● Video compressor (VC)
● USB control block
● General purpose controller
The VP controls the sensor and processes the raw RGB pixel data into YCbCr images.
This YCbCr data is compressed by the VC.
The USB control block transfers the compressed data to the host PC.
1.2 Video processor (VP)
1.2.1 Sensor interface
The VP interfaces directly to the image sensor. The sensor interface comprises:
● 5-wire data bus SDATA[4:0] for receiving both video data and embedded timing references,
● 2-wire serial control interface (SSDA, SSCL),
● sensor clock SCLK
● reset circuitry
● sensor suspend control
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Overview STV0676
Figure 1: Block diagram of STV0676 video processor module
Video Compression (VC) EngineVideo Processor
SDATA[4:0]
SSCL
Compressed Data
Control +
RAM
USB core /glue
logic and
command FIFO’s
10
Clocks
+ PLL
USB port
D+
D-
Digiport
CIF/VGA
Sensor
SSDA
RESET_N
SCLK
SUSPEND
General purpose
housekeeper functions
including AEC, AGC and
AWB
SDA
SCL
RESET
Stream
FIFOs
ROM
8052 Core
STV0676
GPIO/mode
select
10
Ext.
Interrupts
I2C Interface
12MHz
XTAL
1.2.2 Video processor functions
STV0676 provides a master clock SCLK to the camera module. Each 10-bit pixel value generated
by the sensor is transmitted across the 5 wire databus SDATA[4:0] as a pair of sequential 5-bit
nibbles, most significant nibble first . Codes representi ng the start and end fra mes and the start and
end of lines are embedded withi n the video d ata stream to all ow the video processor to synchronise
with the video data stream.
The video processing engine performs the following functions on incoming data:
● full colour restoration at each pixel site from Bayer-patterned input data,
● matrixing/gain on each colour channel for colour purity,
● peaking for image clarity,
● gamma correction,
● colour space conversion from raw RGB to YCbCr[4:2:2].
The 2-wire sensor serial interface (SSDA and SSCL) provides control of sensor configuration.
Note: the MSBit SDATA5 of the databus is unused in the current application but it will support future
sensors where a 12bit ADC architecture may be used.
6/21 Revision C
STV0676 Overview
1.3 Auto exposure and gain control
The STV0676 automatically controls the sensor exposure, which is evaluated (and, where
necessary modified) once per frame, where a frame consists of 2 video fields. The video fields are
identical in length, that is, they do not contain any of the half line detail of the analogue video
standards like CCIR or NTSC. T wo fields per frame are requir ed by the internal sensor video timi ng
model. Integration time, sensor analogue gain and STV0676 digital gain are all used to control the
overall exposure. The STV0676 exposure al gorithm uses an asymptotic ap proach in calculating th e
change required in the present exposure value to approach the requested exposure target.
1.4 Defect correction
STV0676 automatically detects and corrects pixel defects without the need for any additional
components or sensor calibration procedures. This greatly simplifies camera assembly and test
when compared with previous EEPROM-based defect correction schemes. The pixel defect
correction scheme ensures that the STV0676 + ST CMOS sensor appears as a ‘defect free’
chipset.
1.5 Video compression (VC) engine
The video compression engine performs 3 main functions:
● up scaling of input YCbCr 4:2:2 video stream from the VP (typic ally to scale from QVGA to CIF
image formats),
● compression and encoding of YCbCr stream into Motion-JPEG (M-JPEG) format,
● USB bandwidth monitoring.
The data stream from the VP can be up to VGA size. The scaler in VC can downsize this image.
Once scaled the video stream is then converted into M-JPEG format. M-JPEG simply treats video
as a series of JPEG still images. The conversion is realised via a sequential DCT (discrete cosine
transform) with Huffman encoding. After transfer over USB, the M-JPEG stream is decoded in the
device driver running on the host.
The VC module is capable of compression ratios of up to 100:1 although this is scene-dependent.
Image framerate produced by the STV0676 chipset is fixed and furthermore the available USB
bandwidth is also fixed (within the software dri ver) . The VC m odul e varies the compr ession ratio to
match the fluctuating input video data rates to the available USB bandwidth and re quired framerate.
The final stage of the VC block manages the data transfer from the local VC FIFO store to the USB
core. STV0676 performs this ma nagem ent a utoma tical l y by e mpl oyin g long- ter m (fr ame-l evel ) and
short-term (block-level) compression management.
1.6 Control processor
The embedded 8052 microprocessor core controls the data flow through the major sub blocks
within STV0676 as well as the I
from the device driver.
1.7 Power manageme nt
The chipset conforms to all power requirements specified by USB Version 1.1.
2
C communications to reconfigure the VP corresponding to requests
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