LM1236 National Semiconductor Corporation, LM1236 Datasheet - Page 22

• Manufacturer Part Number: LM1236
• Description: 150 Mhz I2c Compatible Rgb Preamplifier With Internal 254 Character Osd Rom, 512 Character Ram And 4 Dacs
• Manufacturer: National Semiconductor Corporation

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OSD Generator Operation
OSD WINDOW FADE IN/ FADE OUT
The OSD window can be opened and closed with a fade
in/fade out effect. The interval for fading in and fading out the
OSD window in the horizontal and vertical direction is vari-
able and can be set by the microcontroller. This allows the
OSD window to be opened or closed in the vertical direc-
tions, horizontal direction, or from the upper left to lower right
corner. Assuming the desired time to typically complete a full
fade in or fade out is 0.5 seconds, and if the vertical scan
frequency is for example, 60 Hz, the number of steps is:
With a typical OSD window that is 300 pixels wide and 180
video lines long, the horizontal and vertical intervals would
be:
For a smooth fade in or fade out animation from the upper
left corner to the lower right corner, the horizontal to vertical
interval ratio must be matched to the aspect ratio of the OSD
window. In the example above, the 300 pixel wide by 180
lines long OSD window has an aspect ratio of 5:3. Thus, the
horizontal to vertical interval ratio should be set to 5/3 or
10/6. With an OSD window aspect ratio of 3:2, the H/V
intervals can be set to 3/2, 6/4, 9/6, 12/8, or 15/10 for optimal
operation. If the calculated aspect ratio of an OSD window is
a non-integer ratio, the H/V interval ratio should meet or
exceed the aspect ratio. For example, if the OSD aspect
ratio is 3.7:2 (or 1.85:1), the H/V intervals should be set to
2/1, 4/2, 6/3, 8/4, 10/5, or 12/6. The fade in/out speed
increases as H/V interval settings are increased. The OSD
window can also be faded in or out in only one direction if
desired, by setting the horizontal interval to 0 for fading in/out
strictly in the vertical direction or setting the vertical interval
to 0 for fading in/out in the horizontal direction. In interlaced
video formats, it is not recommended to fade in and fade out
the OSD in the vertical direction, and should be only faded in
the horizontal direction. The fade in/out function can be
enabled/disabled with bit 5 of the frame control register,
(Continued)
22
0x8400, and the horizontal & vertical intervals are controlled
by setting register 0x8429. The OSD window fade in/out
feature can only be used with OSD window 1.
ENHANCED FEATURES
In addition to the wide selection of colors for each character,
additional character features can be selected on a character
by character basis. There are 3 Enhanced Feature Regis-
ters, EF0, EF1 and EF2.
1. Button Boxes — The OSD generator examines the char-
2. Heavy Button Boxes — When heavy button boxes are
3. Shadowing — Shadowing can be added to two-color
4. Bordering — A border can be added to the two-color
5. Blinking — If blinking is enabled as an attribute, all colors
acter string being displayed and if the “button box” at-
tributes have been set in the Enhanced feature byte,
then a box creator selectively substitutes the character
pixels in either or both the top and left most pixel line or
column with a button box pixel. The shade of the button
box pixel depends upon whether a “depressed” or
“raised” box is required, and can be programmed
through the I
color (“highlight”) is defined by the value in the color
palette register, EF1 (0x8405–0x8406), which is nor-
mally set to white. The depressed pixel (“lowlight”) color
by the value in the color palette register, EF2
(0x8407–0x8408), which is normally set to gray. See
Figure 19 for detail and Figure 20 for the on-screen
effect.
selected, the color palette value stored in register EF3
(0x8409 - 0x840A) is used for the depressed (“lowlight”)
pixel color instead of the value in register EF2.
characters by choosing the appropriate attribute value
for the character. When a character is shadowed, a
shadow pixel is added to the lower right edges of the
color 1 image, as shown in Figure 21 . The color of the
shadow is determined by the value in the color palette
register EF3, which is normally set to black.
characters. When a character is bordered, a border pixel
is added at every horizontal, vertical or diagonal transi-
tion between color 0 and color 1. See Figure 22 . The
color of the border is determined by the value in the color
palette register EF3 (normally black).
within the character except the button box pixels which
have been overwritten will alternately switch to color 0
and then back to the correct color at a rate determined
by the microcontroller through the I
interface.
2
C compatible interface. The raised pixel
2
C compatible