VV0670P001 View Datasheet(PDF) - Vision
Part Name
Description
MFG CO.
'VV0670P001' PDF : 36 Pages View PDF
Colour Processor Interface ASIC
2.2.4 USB Interface
The USB interface is fully compliant with USB Specification Version 1.0. The USB interface is designed such
that the camera attaches to the PC via a 4-wire USB cable, either directly at the PC motherboard USB
connector (root hub) or via a USB hub (in turn connected to the PC motherboard root hub). The USB hub
may be either a stand-alone USB hub device or a compound USB hub device incorporated, for example, in a
USB monitor or printer.
USB transfers both signal and power over the 4-wire cable such that the camera is powered from the same
cable/connector over which it communicates with the PC. The 4-wire cable carries VBus (nominally +5V at
the source) and GND wires to deliver power to devices and differential data lines, D+ and D-. The clock is
transmitted encoded along with the differential data. The clock encoding scheme is NRZI with bit stuffing to
ensure adequate transitions. A SYNC field precedes each packet to allow the receiver(s) to synchronise their
bit recovery clocks. CPiA provides fully compliant USB differential pads on-chip so there is no need to use an
external, discrete bus tranceiver chip such as Philips’ PDIUSBP11. In accordance with the USB Specification
Version 1.0, the pads have been characterised for correct operation up to the maximum peripheral cable
length of 5m.
2.2.4.1 CPiA-Based USB Camera
The CPiA-based USB camera is a high-power, bus-powered device. When it is first attached to a USB hub
port it operates in its low-power mode consuming no more than 100mA. Once the camera has been
successfully enumerated it may operate in its high-power mode in which it consumes no more than 400mA.
Since the camera is a high-power, bus-powered device it will only enumerate successfully if connected to a
self-powered USB hub. (A bus-powered USB hub is only capable of supplying 100mA at each of its
downstream ports).
The CPiA-based USB camera responds to suspend signalling issued by the USB (more than 3ms of bus
IDLE time). In its suspend mode of operation the camera draws no more than 500uA. The camera does not
support remote wakeup.
The CPiA USB camera is a single Configuration, single Interface USB peripheral device. Its single Interface
(Interface 1) supports Control Endpoint 0 and Isochronous IN Endpoint 1.
All devices must support Control Endpoint 0 as this is the endpoint with which the PC communicates over the
default pipe at device enumeration time. CPiA utilises Control Endpoint 0 to respond to standard USB
commands (such as those used at device enumeration time) and to Vendor specific CPiA commands which
are used to control the operation of the camera and to request status information from the camera. Note that
the camera does not support a USB Class Specification and so only Vendor commands are used to control
the operation of the camera.
Isochronous IN Endpoint 1 is used to transfer video data from the camera to the PC. Usin g an isochronous
endpoint for this task guarantees bandwidth and latency for the transfer of video data. The bandwidth
requested for video data transfer can be varied by means of the four defined Alternate Settings of Interface 1.
2.2.4.2 USB Control Transfers
Control transfers are used to pass control information to the CPiA-based USB camera from the host and to
request state information back from the camera. For example, control transfers are used at device
enumeration time when the host PC requests information about the USB device which has been dynamically
attached to the bus to enable it to load the appropriate driver(s). (USB Device Enumeration is discussed in
detail in section 2.2.4.3). CPiA uses Control Endpoint 0 for all control transfers. Therefore Endpoint 0 handles
both standard USB commands and Vendor specific CPiA commands.
A control transfer consists of three phases: a SETUP phase, a DATA phase (should one exist) and a STATUS
phase.
V:\apps\cpia\docs\cpia datasheet\cpia_datasheet4.fm
02/07/98
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