VV0670P001 View Datasheet(PDF) - Vision
Part Name
Description
MFG CO.
'VV0670P001' PDF : 36 Pages View PDF
Colour Processor Interface ASIC
2.2.5.12 Image Stream Transfers
Transfers of image stream data are distinguished from those of the command and status data by the use of a
slightly different negotiation phase preceeding the transfer. Image stream transfers operates only in the
reverse direction i.e. CPiA to host.
All image stream transfers are preceeded by a 1284 negotiation sequence which sets the "extensiblity link
request" bit within the first Extensibility Request Value. The subsequent Extensiblity Request Value then
determines which of two possible transfer modes will be used to transfered the data. Ima ge Stream transfers
are terminated with the standard 1284 termination sequence.
The protocol used to transfer the data depends on the capabilites of the host. If it has an ECP parallel port
then the standard ECP byte level protocol is used. However, if it has a bi-directional, or 4 bit port, then a
modified form of the 1284 Nibble mode transfer is used. This modified form, refered to hereafter as a Nibble
Stream mode , is used in preference to the standard nibble mode to improve the maximum transfer rate.
Nibble Stream mode differs from standard Nibble mode by the fact that both the rising and falling edges of the
nAutoFd signal are used to clock data.
The diagram below shows the negotiation sequence that proceeds a Nibble Stream Mode transfer, and the
start of of the actual image data transfer.
NOTE - Requests by the host for Nibble Stream or ECP Stream mode transfers can be easily disguished
from standard Nibble Mode and ECP negotiations by the double nStrobe low pulses that occur during the
negotiation phase.
Figure 2.13 : Typical Nibble Stream Negotiation
100 µ s Div
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