LM1247 National Semiconductor, LM1247 Datasheet - Page 42

• Manufacturer Part Number: LM1247
• Description: 150 MHz I2C Compatible RGB Preamplifier with Internal 512 Character OSD ROM, 512 Character RAM and 4 DACs
• Manufacturer: National Semiconductor

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Attribute Table and Enhanced Features
BUTTON BOX FORMATION
The value of the most significant Enhanced Feature Bit
(EFB3) determines when to draw the left, right, bottom and
top sides of a Box. EFB1 denotes whether a box is raised or
depressed, and EFB2 denotes whether the box is normal or
“heavy”. For normal boxes, the lowlight color is determined
by the color code stored in the register EF2. For the heavy
box feature, the lowlight is determined by the color code
stored in register EF3. Boxes are created by a “pixel over-
ride” system that overwrites character cell pixel information
with either the highlight color (EF1) or low light shadow (EF2
or EF3) of the box. Only the top pixel line of the character
and the right edge of the character can be overwritten by the
pixel override system.
To form a complete box, the left hand edge of a box is
created by overwriting the pixels in the right most column of
the preceding character to one being enclosed by the box.
The bottom edge of a box is created by either —
Characters should be designed so that button boxes will not
interfere with the character.
These are the limitations resulting from the button box for-
mation methodology:
• overwriting the pixels in the top line of the character
• overwriting the pixels in the top line of the skipped lines
• No box may use the left most display character in the
• At least one skip line must be used beneath characters
• Skipped lines cannot be used within a box covering sev-
• Irregular shaped boxes, (i.e., other than rectangular),
Attribute Number, (n)
below the character being enclosed by the box, or
below, in the case where skip lines are present below a
boxed character.
Display Window, or it will have no left side of the Box. To
create a box around the left most displayed character, a
transparent “blank” character must be used in the first
character position. This character will not be visible on
the screen, but allows the formation of the box.
on the bottom row, if a box is required around any char-
acters on this row in order to accommodate the bottom
edge of the box.
eral rows.
may have some missing edges.
0100b
0101b
0110b
1000b
1001b
1010b
1011b
1100b
1101b
0111b
1110b
1111b
TABLE 25. Attribute Tables and Corresponding Addresses (Continued)
Two-Color Attribute Table Address
0x845C–0x845F
0x846C–0x846F
0x847C–0x847F
0x8458–0x845B
0x8468–0x846B
0x8478–0x847B
0x8450–0x8453
0x8454–0x8457
0x8460–0x8463
0x8464–0x8467
0x8470–0x8473
0x8474–0x8477
42
Operation of the Shadow Feature
The shadow feature is created as follows: As each 12-bit line
in the character is called from ROM, the line immediately
preceding it is also called and used to create a “pixel over-
ride” mask. Bits 11 through 1 of the preceding line are
compared to bits 10 through 0 of the current character line.
Each bit X in the current line is compared to bit X+1 in the
preceding line (i.e., the pixel above and to the left of the
current pixel). Note that bit 11 of the current line cannot be
shadowed. A pixel override output mask is then created.
When a pixel override output is 1 for a given pixel position,
the color of that pixel must be substituted with the color code
stored in the register EF3. Please see Figure 28 for an
example.
Operation of the Bordering Feature
Borders are created in a similar manner to the shadows,
using the pixel override system to overwrite pixel data with a
pixel color set by EF3. However, instead of comparing just
the previous line to the current line, all pixels surrounding a
given pixel are examined.
The pixel override is created as follows: As each 12-bit line in
the character is called from ROM, the character line imme-
diately above and the line immediately below are also called.
A “Pixel Override” output mask is then created by looking at
(Continued)
FIGURE 28. Operation of the Shadow Feature
Four-Color Attribute Table Address
0x8520–0x8527
0x8528–0x852F
0x8530–0x8537
0x8538–0x853F
0x8540–0x8547
0x8548–0x854F
0x8550–0x8557
0x8558–0x855F
0x8560–0x8567
0x8568–0x856F
0x8570–0x8577
0x8578–0x857F
20048443