% -*- Mode:Text -*- 
% PROGRAMMABLE MATTER (DOE proposal, 1992)

 \input packbook.sty

 \input sorspath
 \def\runninghead{{\footnotesize {\em CAM-8 Video Output}
    \qquad DRAFT, \today\qquad {\tt\sourcepath/\jobname}}}

 \input comment.sty
 \input notecomm
 \input cam8spec

 \begin{document}

 \chapter{VGA and Video Output}

 \section{Generalities}

Each \cam{} box has dedicated display circuitry consisting of a frame
grabber and separate display encoders for analog \vga{} and video
outputs; frame timing and video encoding may be programmed for either
\ntsc{} or \pal{} format.\footnote
	{Since the same field rate is used for \vga{} and video, in
\pal{} mode the \vga{} signal will have a (nonstandard) vertical
frequency of 50 Hz and may not be usable by all \vga{} monitors.}
	Video output is available both as ordinary video (a single
channel with baseband luminance and color on a color carrier) and as
S-video (two baseband channels, one for luminance and one for chroma).

Display processing is performed by the box interface. The information
to be displayed, along with display control information, is provided
to it by module 0 via eight data lines ({\sym Disp[0..7]}) and four
control lines ({\sym DispValid*}, {\sym Sync}, {\sym Capture*}, and
{\sym Reset}).

{\sym DispValid} is used as a ``data enable'' signal associated with
the {\sym Disp} lines: valid data are present on these lines only on
clock cycles in which {\sym DispValid} is asserted. {\sym Sync}
provides the information from which the monitors' horizontal and
vertical sync pulses are derived. A steady asserted value for {\sym
Capture} indicates that a new image frame is present on the {\sym
Disp} lines and should be captured by the frame grabber; a steady
unasserted value signifies that \cam{} is not supplying image data,
and the video image should be refreshed with the data held in the
frame grabber.

An isolated {\sym Capture} pulse initiates the downloading of color
data to the video palette; the data are supplied by the host and
relayed by module 0 via the {\sym Disp} lines. Finally, every time the
\cam{} system comes out of {\sym Reset}, the display circuitry goes
through a re-initialization sequence, using data supplied by the host
in the same manner.


\section{VGA output}



\section{Video output}

A video {\em frame} consists of two interlaced {\em fields}. Each
field lasts as long as a \vga{} frame (1/60 sec in \ntsc{} mode);
however, it contains half as many lines (the even line on even fields,
and the odd lines on odd fields), each consisting of as many pixels as
a \vga{} line but sent at half the rate. To make a video field from a
\vga{} frame, we discard every other \vga{} line. The lines we keep
(respectively, even and odd on even and odd fields) are then stretched
by a factor of two.


\subsection{Programming the Bt858}






 \end{document}
