PRELIMINARY

Digital Camera Chipset; Customer Datasheet, Rev 3.0, March 2000

STV0680A + VV6444/6410/6500

CDSTV0680F-C

Commercial in confidence

20

STV0680F_contents.fm

refresh from STV0680A takes place.

4.3.4

SDRAM initialisation Period

The SDRAM initialisation period is currently set to 981

µS in STV0680A.

4.4

USB interface

STV0680A includes a USB Version 1.1 compliant Universal Serial Bus Interface, including a transceiver. This allows direct

connection from STV0680A to a USB connector with minimal additional hardware (i.e. a small number of passive discretes) - see

Section 9.

The USB interface interfaces the STV0680A to the USB at full speed 12MHz data rate. Some of the features are:

•

Compliant with USB protocol revision 1.1.

•

USB protocol handling.

•

USB device state handling.

•

Clock and data recovery from USB.

•

Bit stripping and bit stuffing functions.

•

CRC5 checking, CRC16 generation and checking.

•

Serial to parallel conversion.

•

Single bulk end point.

USB drivers are supplied by ST. For USB timing information, please refer to the USB specification V1.1.

4.5

UART module for RS232 interface

The UART module on STV0680A provides a 115200 baud full duplex interface to an external Host.

4.5.1

RS232 Physical interface

STV0680A does not support direct connection to a serial link. Physical line driver circuitry is required, e.g. using a standard

RS232 transceiver chip, or by using a small number of low cost discretes (as shown in Section 9.). The schematics shown

assume a 3 core cable with a length of no greater than 2m. Unscreened cable can be used, a suitable low cost connector is a

3.5mm audio jack plugs/sockets.

4.5.2

UART Module Overview

Receiving data

The UART module in STV0680A receives serial data through the RXD pin. Data reception is initiated by a 1-to-0 transition on

RXD, and the received data is sampled every 8.66

µS.

If the RXD input is not 0 when the incoming data is first sampled, the UART module goes back to look for another 1-to-0

transition. This is to provide rejection of false start bits. If the start bit proves valid, reception of the rest of the frame will proceed.

Transmitting data

When a transmission is activated by STV0680A, the contents of an internal transmit shift register are shifted onto the TXD pin,

every 8.66

µS.

The UART operates at 12MHz, which is not an integer multiple of 115200, so the actual baud rate is 115232 +/- 0.3%, which is

well within the requirements of a typical 16x oversampling UART, which can tolerate a 3.75% error in baud rate.

4.6

Power management and battery type

STV0680A and the SDRAM require a 3.3V supply. Where a VV6410 or VV6500 (3.3v) sensor is used, a single voltage regulator

can be used to regulate the supply for all three components from the battery, or the sensor on-board VReg can be used. Where a

VV6444 is used, the sensor requires a 5V supply, hence a DC-DC converter is recommended to provide enough voltage when

the camera is powered from the USB bus. These are explained more fully in the reference design.