October 2002

ADCS 7280926C

1/21

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, RGB-
preview, 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.

STMicroelectronics offers camera manufacturers
rapid-to-market camera products supported by
comprehensive reference designs, software drivers
and technical backup.

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 white balance

APPLICATIONS

USB camera:

- Biometric identification, toys and games

Embedded applications support:

- PDA, notebook PC, mobile phone

- Set top box, and security applications

Typical application

CMOS Sensor

CIF or VGA

lens + IR filter

to host PC

USB Cable

STV0676

EEPROM

image

array

MIcro

Processor

USB

Interface

Video

Compression

Video

Processor

STV0676

2/21

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

5/21

STV0676

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 capable of transferring 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

Overview

STV0676

6/21

Revision C

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 representing the start and end frames and the start and
end of lines are embedded within the video data stream to allow 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.

Figure 1: Block diagram of STV0676 video processor module

Video Compression (VC) Engine

Video Processor

Stream

Digiport

D+

D-

Clocks

+ PLL

12MHz

XTAL

8052 Core

ROM

GPIO/mode

STV0676

RAM

Compressed Data

Control +

FIFOs

Ext.

Interrupts

CIF/VGA

Sensor

C Interface

USB core /glue

logic and

command FIFO's

General purpose

housekeeper functions
including AEC, AGC and

AWB

SDA

SCL

RESET

SDATA[4:0]

SSCL

SSDA

RESET_N

SCLK

SUSPEND

select

USB port

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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. Two fields per frame are required by the internal sensor video timing
model. Integration time, sensor analogue gain and STV0676 digital gain are all used to control the
overall exposure. The STV0676 exposure algorithm uses an asymptotic approach in calculating the
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 (typically 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 driver). The VC module varies the compression ratio to
match the fluctuating input video data rates to the available USB bandwidth and required 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 management automatically by employing long-term (frame-level) 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

C communications to reconfigure the VP corresponding to requests

from the device driver.

1.7

Power management

The chipset conforms to all power requirements specified by USB Version 1.1.

External interfaces

STV0676

8/21

Revision C

External interfaces

2.1

USB interface

The USB interface is designed to be compliant with version 1.1 of the USB specification. The
STV0676 is a low power device and is therefore suitable for connection to any USB port on a PC,
self-powered hub or when connected to a bus-powered hub.

The device complies with the device framework specified in Chapter 9 of the USB specification as
follows:

The device supports a single high power configuration (

Configuration 1

Endpoint 0 is the default control endpoint and is always supported.

Endpoint 0 supports all of the USB commands required by the device framework.

Vendor specific commands on Endpoint 0 are used for all device control.

Configuration 1 supports a single interface (interface 0).

Interface 0 supports 8 alternate settings (alternates 0-7).

The alternate settings support between 0 and 2 additional endpoints.

Endpoint 1 is used for isochronous transfer of image data.

Endpoint 3 is used for transferring status information, e.g. state of a hardware button.

The endpoints are configured as follows (

Table 2

) in the alternate settings:

The best and most consistent performance in terms of image quality is always obtained in the
highest bandwidth setting (alternate 7). Under some circumstances it may not be possible for the
host to allocate this amount of USB bandwidth to the device.

The isochronous settings reserve varying quantities of bandwidth - from 10% to 85% of USB
bandwidth. The lower settings result in poor image quality due to heavy compression applied to
maintain a high framerate streaming of image data, but at the same time leaving more bandwidth
free for other USB devices. This is desirable if more than one camera is to be used, or if there are
other isochronous peripherals connected. The device driver allows the user to specify the maximum
bandwidth they wish to allocate to transfer data from the device. If the maximum specified by the
user is not available, perhaps because another isochronous device has already reserved that
bandwidth, then lower alternates are tried until one succeeds.

Table 2: Endpoint alternate settings

Alternate setting

Endpoint1 (isochronous)

Endpoint3 (interrupt)

Not present

8 bytes / packet; 1 packet /8 frames

128 bytes / packet; 1 packet / frame

8 bytes / packet; 1 packet /8 frames

384 bytes / packet; 1 packet / frame

8 bytes / packet; 1 packet /8 frames

640 bytes / packet; 1 packet / frame

8 bytes / packet; 1 packet /8 frames

768 bytes / packet; 1 packet / frame

8 bytes / packet; 1 packet /8 frames

896 bytes / packet; 1 packet / frame

8 bytes / packet; 1 packet /8 frames

1023 bytes / packet; 1 packet / frame

8 bytes / packet; 1 packet /8 frames

9/21

STV0676

External interfaces

Benchmark testing of the STV0676 indicates that 30fps CIF video (compressed) can be
accommodated in 50% of USB bandwidth.

2.2

Mode selection

All USB devices report a VID, PID and power consumption as part of a standard device descriptor.
The VID and PID for STV0676 can be configured by the state of the digiport bits or by using an
external EEPROM. The mode selection is made using the two MODESEL pins as described in

Table 3

below.

2.3

Selecting VID and PID via the digiport

Tables 4~7 demonstrate how the VID/PID information is defined via the digiport.

The current reference design for the STV0676-chipset has digiport[7:0] connected to VSS, thus the
VID and PID are 16'h0553 and 16'h0140 respectively.

The digiport also controls the device current consumption that is reported to the host at device
enumeration.

Table 3: Mode selection

MODESEL[1]

MODESEL[0]

Mode of operation

USB Mode. External EEPROM fitted, therefore PID, VID and power
consumption read from this source. See

Section 2.4

Slave I

C mode.

USB mode. Default. No external EEPROM fitted, the PID
VID and power consumption data determined by digiport[7:0].
See

Section 2.3

Reserved

Table 4: Basic digiport configuration

digiport bit slice

function

[3:0]

configures the LS nibble of the PID

[5:4]

master VID/PID select

[7:6]

power setting

Table 5: Digiport LS nibble configuration

digiport[3:0]

PID LS nibble

4'b0000

4'b0001

4'b0010

4'b0011

4'b0100

4'b0101

External interfaces

STV0676

10/21

Revision C

2.4

Serial EEPROM

STV0676 is designed to be used with a 128 or 256 byte serial I

C EEPROM. The EEPROM can be

programmed with data to allow a user to fully customise the USB identity of STV0676. The
configuration of this data is as follows.

4'b0110

4'b0111

4'b1000

4'b1001

4'b1010

4'b1011

4'b1100

4'b1101

4'b1110

4'b1111

Table 6: Master VID/PID selection

digiport[5:4]

VID/PID reported

2'b00

16'h0553/16'h014x

2'b01

16'h0553/16'h015x

2'b10

16'h0553/16'h026x

2'b11

16'h0553/16'h017x

a. The `x' ls nibble of the PID is defined by the value from

Table 5

above

Table 7: Device power consumption indicator

digiport[7:6]

current consumption reported

2'b00

98mA

2'b01

250mA

2'b10

350mA

2'b11

500mA

Table 5: Digiport LS nibble configuration

digiport[3:0]

PID LS nibble

11/21

STV0676

External interfaces

2.4.1

EEPROM format and contents

The remaining space is available for the string blocks indexed at locations 8, 9 and 10.

2.4.2

Strings

The strings referred to above (locations 8-10), are the USB string descriptors referenced from the
device, configuration and interface descriptors. The value should be set to '0' if the string is not
implemented or to the offset in bytes of the start of the string block in the EEPROM.

The first byte of each string block is the number of the characters in the string. Subsequent bytes
are the actual string, which need not include a terminating null (

Table 9

:).

Table 8: EEPROM format and contents

location

contents

fixed number, must be 0x'ED

fixed number, must be 0x'15

reserved, must be 0x'00

max device power (=mA/2, e.g. 400mA enter 0x'C8)

VidLo, low byte of the vendor ID

VidHi, highbyte of the vendor ID

PidLo, low byte of the product ID

PidHi, highbyte of the product ID

manufacturer string offset, example below

product string offset, see below

interface 0 String offset

reserved, must be 0x'00

checksum

Table 9: EEPROM device string example

Location

Contents

Manufacturer string offset = 16

String length = 5

String text = `H' (in ascii)

String text = `e' (in ascii)

String text = `l' (in ascii)

String text = `o' (in ascii)

External interfaces

STV0676

12/21

Revision C

2.4.3

CheckSum

The checksum is calculated by adding the byte value of EEPROM locations 0 to 12 inclusive, the
low order byte of the result is stored in location 13.

2.5

C slave mode

STV0676 can be configured to behave as an I

C slave. This allows the device to be configured by

host devices other than PCs. Details of the I

C messages supported and description of the I

2.6

Digiport

The Digiport is a 10-bit bi-directional data port which can be used to transfer video data in or out of
the device. This port can also be used to configure USB descriptor information at power up see
(

Section 2.3

). Full details on the digiport operation and control are available from

STMicroelectronics.

2.7

General purpose input and output

STV0676 provides up to 8 pins which can be used as general purpose I/O. These pins can be used
to interface to led's, buzzers, switches etc.

13/21

STV0676

STV0676 application example

3.1

USB webcam

Figure 2

shows a block diagram of a basic webcam using the minimum of external components.

The camera is controlled entirely through PC drivers over USB.

Note:

If required a custom USB PID/VID can be configured by the use of an EEPROM, as detailed in

Section 2.3

3.2

Embedded camera

Figure 3

shows a block diagram of a camera intended for embedded applications, outputting JPEG,

YCrCb or RGB preview over an 8bit bus, the third party electronics would control the STV0676
using I

Figure 2: Webcam block diagram

Figure 3: Embedded camera block diagram

CMOS Sensor

CIF or VGA

lens + IR filter

to host PC

USB Cable

STV0676

EEPROM

image

array

MIcro

Processor

USB

Interface

Video

Compression

Video

Processor

CMOS Sensor

CIF or VGA

lens + IR filter

STV0676

image

array

MIcro

Processor

FIFO

Video

Compression

Video

Processor

Digiport

Third party

electronics

Detailed specifications

STV0676

14/21

Detailed specifications

4.1

STV0676 absolute maximum ratings

4.2

STV0676 AC/DC characteristic

Description

Range

Unit

Operating Temperature

0 to 70

Storage Temperature

-50 to 150

Parameter

Description

Min

Typ

Max

Units

VDD_CORE

Primary STV0676 power supply

1.55

1.8

1.95

VDD_IO

3.3V power supply for on-chip USB transceiver and IO

3.0

3.3

3.6

VDD_PLL

Analog supply to the PLL

1.60

1.8

2.0

I_core

suspend

Current consumption in suspend mode

µA

I_core

standby

Current consumption in standby mode

9.6

I_core

active

Current consumption while active, VGA 30fps

I_IO

suspend

Current consumption in suspend mode

µA

I_IO

standby

Current consumption in standby mode

540

µA

I_IO

active

Current consumption while active, VGA 30fps

6.6

I_PLL

suspend

Current consumption in suspend mode

0.4

µA

I_PLL

standby

Current consumption in standby mode

476

µA

I_PLL

active

Current consumption while active, VGA 30fps

476

µA

CMOS input low voltage (XTAL_IN)

0.687

CMOS input high voltage (XTAL_IN)

1.19

HYS

Hysteresis (XTAL_IN)

0.51

CMOS input low voltage

0.35VDD

CMOS input high voltage

0.65VDD

T+

CMOS schmitt input low to high threshold voltage

2.15

T-

CMOS schmitt input high to low threshold voltage

1.05

Threshold point

1.65

Output high voltage

2.4

Output low voltage

0.4

15/21

STV0676

Pinout and pin descriptions

5.1

STV0676 pin details

Figure 4: STV0676 pinout

IO_VDD
SW0_N

IO_

CORE_V

TEST_CONF[1]

USB

PRO

USB

PLL_VDD

PLL_VSS

XTAL_IN

XTAL_OUT

CORE_VSS

IO_VDD

IO_VSS

DIGIPORT[9]

RESET_N

GPIO[7]

IO_VSS

[2]

SW1_N

SSDA

SSCL

IO_

DIGIPORT[5]

CORE_VDD

TEST_CONF[0]

TEST_CONF[2]

SPDN

CORE

_VDD

ESE

[
1]

IO_V

ED[

]

DIGIPORT[7]

DIGIPORT[8]

DIGIPORT[6]

[4]

[3]

SER

]

DIGIP

[
4]

[
3

]

DIGIP

[
2]

DIGIP

[
1]

[
0

]

IO_V

CORE

_VDD

OR_CLK

OR_DB

[
5]

OR_DB

[
4]

OR_DB

[
3]

OR_DB

[
2]

OR_DB

[
1]

OR_DB

[
0]

GPIO[6]
GPIO[5]
GPIO[4]
GPIO[3]
GPIO[2]
GPIO[1]
GPIO[0]

Pinout and pin descriptions

STV0676

16/21

Table 10: STV0676 pin description

Pin

Signal

Type

Description

POWER SUPPLIES

PLL_VDD

INPUT

VDD for internal phase locked loop

PLL_VSS

INPUT

GND for internal phase locked loop

CORE_VDD

INPUT

VDD for core logic

CORE_VSS

INPUT

Ground for core logic

IO_VDD

INPUT

VDD for pad ring

IO_VSS

INPUT

Ground for pad ring

IO_VDD

INPUT

VDD for pad ring

IO_VSS

INPUT

Ground for pad ring

CORE_VDD

INPUT

VDD for core logic

CORE_VSS

INPUT

Ground for core logic

IO_VDD

INPUT

VDD for pad ring

IO_VSS

INPUT

Ground for pad ring

IO_VSS

INPUT

Ground for pad ring

IO_VDD

INPUT

VDD for pad ring

IO_VSS

INPUT

Ground for pad ring

CORE_VDD

INPUT

VDD for core logic

CORE_VSS

INPUT

Ground for core logic

DEVICE MASTER CLOCK AND RESET

XTAL_IN

ANA

System clock pad

XTAL_OUT

OSC

System clock pad

RESET_N

SCHMITT

System, power-on-reset supplied by companion sensor

DIGIPORT/USB CONFIGURATION INTERFACE

DIGIPORT[9]

BIDIR

Digiport operation

DIGIPORT[8]

BIDIR

Digiport operation

DIGIPORT[7]

BIDIR

Digiport operation /programmable USB current consumption reported

DIGIPORT[6]

BIDIR

Digiport operation /programmable USB current consumption reported

DIGIPORT[5]

BIDIR

Digiport operation /programmable USB VID/PID

DIGIPORT[4]

BIDIR

Digiport operation /programmable USB VID/PID

DIGIPORT[3]

BIDIR

Digiport operation /programmable USB PID

DIGIPORT[2]

BIDIR

Digiport operation /programmable USB PID

DIGIPORT[1]

BIDIR

Digiport operation /programmable USB PID

DIGIPORT[0]

BIDIR

Digiport operation /programmable USB PID

SENSOR INTERFACE

SENSOR_CLK

BIDIR

Sensor clock

17/21

STV0676

Pinout and pin descriptions

SENSOR_DB[5]

INPUT

Sensor data bus [bit5]

SENSOR_DB[4]

INPUT

Sensor data bus [bit4]

SENSOR_DB[3]

INPUT

Sensor data bus [bit3]

SENSOR_DB[2]

INPUT

Sensor data bus [bit2]

SENSOR_DB[1]

INPUT

Sensor data bus [bit1]

SENSOR_DB[0]

INPUT

Sensor data bus [bit0]

SSDA

3 state

Sensor serial interface data

SSCL

3 state

Sensor serial interface clock

SPDN

BIDIR

Control line to sensor to select ultra low power SUSPEND mode

MISC CONTROL

SW1 _N

INPUT

Spare switch input

SW0 _N

INPUT

Remote wakeup

GPIO INTERFACE/ OTHER

GPIO[0]

BIDIR