STV-DCA/CIF-E01 STMICROELECTRONICS [STMicroelectronics], STV-DCA/CIF-E01 Datasheet - Page 23

• Manufacturer Part Number: STV-DCA/CIF-E01
• Description: DUAL-MODE DIGITAL CAMERA CHIPSET
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

STV0680B + VV6444/6410/6500
4.5
4.5.1
4.5.2
4.6
4.6.1
4.6.2
UART module for RS232 interface
The UART module on STV0680B provides a 115200 baud full duplex interface to an external Host.
RS232 physical interface
STV0680B 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
no greater than 2m. Unscreened cable can be used, a suitable low cost connector is a 3.5mm audio
jack plugs/sockets.
UART module overview
Receiving data
The UART module in STV0680B 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 S.
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 STV0680B, the contents of an internal transmit shift register
are shifted onto the TXD pin, every 8.66 S.
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.
Power management and battery type
STV0680B and the SDRAM require a 3.3V supply. Where a VV6410/6411 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.
Power switching to USB
Included in the USB compliance requirements, is the ability of the camera to report to the PC when
connected to the USB bus, whether or not there is a fresh battery in the camera. This means that
power sourcing from USB is required, which also saves on battery life while the camera is used in
USB tethered video mode. In order to allow switching from battery to USB power, some additional
hardware is required (see also
For precise USB compliance requirements, please consult the USB specification version 1.1
Switched sensor supply
Dependant on the hardware implementation, the SENSPWR output from STV0680B can be used to
power off completely the sensor during Standby mode (in the case of VV6444) or put the sensor
battery/battery not fitted. This may be necessary to comply with the USB specification.
The USBDETECT input to STV0680B is used to detect that a USB power supply is connected
If the USB is detected, additional hardware is used to switch off the battery
An inrush protection circuit can protect the USB bus from current draw in the case of a low
Chapter 6
Chapter 6
). The schematics shown assume a 3 core cable with a length of
Version 3.4
):
STV0680B hardware interfaces
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