VV0670P001 View Datasheet(PDF) - Vision
Part Name
Description
MFG CO.
'VV0670P001' PDF : 36 Pages View PDF
Colour Processor Interface ASIC
The diagram below shows the negotiation sequence that proceeds a ECP Stream Mode transfer, no actual
bytes are shown being transfered.
Figure 2.14 : Typical ECP Stream Negotiation
50 µ s Div
Notes on Image Stream Transfers
CPiA produces a low going pulse, of approximately 200 µ s, on the nAck line when image stream data is
available to upload. If the host driver can use this pulse to trigger a parallel port interrupt service routine to
start the the image transfer process.
When the device is sending compressed image stream to the host the amount of data to be sent for each
frame can vary, depending on the compression ratio achieved. So that the host can detect the end of valid
data the device inserts a stream of 0xFF values into the image stream after the host reads past the end the
valid image data. As a sequence of four 0xFF values will never occur within a valid frame of image data the
host can use this to simply detect the end of the image data, without having to decompress the image.
The host driver checks the intergrity of the image data stream before it is decoded, if any corruption is
detected the frame is discarded and another uploaded.
If, while uploading uncompressed images, the transfer of data is monitored via an osciliscope, or logic
analyser, it will be seen there are regular short pauses in the transfer, in the order of 200µ s to 2m s each.
These are caused by the host driver suspending the transfer w hile it copies data out of it’s tem porary buffer
into the target fram e buffer.
V:\apps\cpia\docs\cpia datasheet\cpia_datasheet4.fm
02/07/98
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Commercial In Confidence
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