STV-USB-CIF-R01 Ver la hoja de datos (PDF) - STMicroelectronics
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STV-USB-CIF-R01 Datasheet PDF : 41 Pages
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STV0672-chipsetf-3-1.fm
External Interfaces
3. External Interfaces
3.1 USB Interface
The USB Interface is designed to be compliant with the Version 1.1 of the USB Specification. The STV0672 chipset solution is a
High Power Device and is therefore suitable for connection to any USB port on a PC or on a self-powered hub. It will not function
when connected to a bus-powered hub as there may be insufficient power available.
The device fits into 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 in the alternate settings:
Alternate Setting
0
1
2
3
4
5
6
7
Endpoint1 (Isochronous)
Endpoint3 (Interrupt)
Not present
Not present
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
Table 3 : Endpoint Alternate Settings
The best and most consistent performance in terms of image quality will always be 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 will
give poor image quality due to heavy compression applied to maintain high framerate streaming of image data, but at the same
time will leave more bandwidth free for other USB devices. This may be more 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 data transfer 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 will be tried until one succeeds.
Benchmark testing of the STV0672 indicates that 30fps CIF video (compressed) can be accomodated in 50% of USB bandwidth.
3.2 USB Vendor ID (VID) and Product ID (PID)
All USB devices will report a VID and PID as part of a Standard Device Descriptor. The VID and PID for STV0672 are configured
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29 November 2000
Commercial in confidence
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