SAA7102 Datasheet, PDF (16/76 Pages) NXP Semiconductors – Digital video encoder

Philips Semiconductors
Digital video encoder
Product specification
SAA7102; SAA7103
Most TV sets use overscan, and not all pixels respectively
lines are visible. There is no standard for the factor, it is
highly recommended to make the number of output pixels
and lines adjustable. A reasonable underscan factor is
10%, giving approximately 640 output pixels per line.
The total number of pixel clocks per line and the input
horizontal offset need to be chosen next. The only
constraint is that the horizontal blanking has at least
10 clock pulses.
The required pixel clock frequency can be determined in
the following way: Due to the limited internal FIFO size, the
input path has to provide all pixels in the same time frame
as the encoders vertical active time. The scaler also has to
process the first and last border lines for the anti-flicker
function. Thus:
TPclk = -----------------2---6---2----.-5-----^×-----1----7---1----6----^×-----T----X----c---l-k----------------- (60 Hz)
InPpl × integer_^{I--n-O---L--u-i-n-t--L--+}-i-n---2-- × 262.5_
TPclk = -----------------3---1---2----.-5-----^×-----1----7---2----8----^×-----T----X----c---l-k----------------- (50 Hz)
InPpl × integer_^{I--n-O---L--u-i-n-t--L--+}-i-n---2-- × 312.5_
and for the pixel clock generator PCL = ^{TT----XP----cc---ll--kk-} × 2²¹
(all frequencies); see Table 80.
The input vertical offset can be taken from the assumption
that the scaler should just have finished writing the first line
when the encoder starts reading it:
YOFS = ^{F----A----L-I--n--×}-P----1p----l7--_×-1---6-T----P^×----c-T--l-k-X----c---l-k-- – 2 (60 Hz)
YOFS = ^{F----A----L-I--n--×}-P----1p----l7--_×-2---8-T----P^×----c-T--l-k-X----c---l-k-- – 2 (50 Hz)
In most cases the vertical offsets will be the same for odd
and even fields. The results should be rounded down.
Once the timings are known the scaler can be
programmed.
XOFS can be chosen arbitrarily, the condition being that
XOFS + XPIX ≤ HLEN is fulfilled. Values given by the
VESA display timings are preferred.
HLEN = InPpl − 1 XPIX = ^{I--n----2P----i-x-} XINC = ^{O---I--nu---P-t-P--i-x-i--x-} × 4096
XINC needs to be rounded up, it needs to be set to 0 for a
scaling factor of 1.
YPIX = InLin
YSKIP defines the anti-flicker function. 0 means maximum
flicker reduction but minimum vertical bandwidth, 4095
gives no flicker reduction and maximum bandwidth.
YINC = _{I--n-O---L--u-i-n-t--L--+}-i-n---2-- × _1 + ^{Y--4---S-0---K-9---I5-P---}_ × 4096
YIWGTO = ^{Y-----I-2N-----C--} + 2048
YIWGTE = ^{Y-----I-N-----C-----–}--2---Y----S----K----I--P--
When YINC = 0 it sets the scaler to scaling factor 1. The
initial weighting factors must not be set to 0 in this case.
YIWGTE may go negative. In this event, YINC should be
added and YOFSE incremented. This can be repeated as
often as necessary to make YIWGTE positive.
Due to the limited amount of memory it is not possible to
get valid vertical scaler settings only from the formulae
above. In some cases it is necessary to adjust the vertical
offsets or the scaler increment to get valid settings.
Tables 6 to 23 show verified settings. They are organised
in the following way: The tables are separate for the
standard to be encoded, the input resolution and three
different anti-flicker filter settings. Each table contains
5 vertical sizes with 5 different offsets. They are intended
to be selected according to the current TV set. The
corresponding horizontal resolutions of 640 pixels give
proper aspect ratios. They can be adjusted according to
the formulae above. The next line gives a minimum size
intended to fit on the screen under all circumstances. The
corresponding horizontal resolution is 620 pixels.
Overscan is only possible with an input resolution of
800 × 600 pixels. Where possible, the corresponding
settings are given on the last lines of the tables.
2001 Sep 25
16