Technical data

Signal Descriptions
5
Video Clocks (CLK_2_{H,L}, CLK_2_QUAD_{H,L})
To control in-flight skew between clock and data caused by nonuniform group delay in
the cable, it is important to carefully match the spectral characteristics of the clocks to the
data transmitted on the DVP interface. This is accomplished by transmitting an in-phase
and a quadrature-phase version of the pixel clock, divided by 2. (See Figure 1-4 for
Silicon Graphics recommendations for recovering a full-speed pixel clock on the receiver.
See Figure 1-5 for Timing Diagram information.)
Timing Signals
CBLANK_{H,L}, CSYNC_{H,L}, VSYNC_{H,L}, FIELD_{H,L} indicate the structure of
the video raster being transmitted by the DVP interface. Except for CBLANK_{H,L} and
FIELD_{H,L}, these signals are user-programmable via the Video Format Compiler. (For
more information, see the InfiniteReality Video Format Compiler Programming Guide, part
number 007-3402-001). CBLANK serves as an indicator of active video. It has a fixed,
non-programmable, 3-pixel clock skew with respect to video. CBLANK will transition
active/inactive 3 pixel clocks (3 edges of CLK_2_QUAD) before video data. The skew
allows for easy implementation of control circuits in the receiver. FIELD_{H,L} indicates
the field that is currently being transmitted. For non-interlaced video formats, FIELD_H
is always inactive (low). For interlaced formats, FIELD_H is always active (high)
throughout the second field of the frame.
Framebuffer Swap Information (VOC_SWAP)
The VOC_SWAP signal indicates the first frame of video that occurs after the framebuffer
memory has been swapped. This is the default semantics of this signal. VOC_SWAP is
actually a catch-all signal. It may be statically programmed to send any one of the
following 6 video signals:
• line-start
•field-start
• frame-start
• tri-sync (useful for generating analog HDTV signals)
• vdrc-enable (the window during which the VOC is allowed to request video data
from the framebuffer. VOC_SWAP is actually vdrc_en, conditioned with a latched
version of the framebuffer swap signal).