z86229 ZiLOG Semiconductor, z86229 Datasheet - Page 12

• Manufacturer Part Number: z86229
• Description: Z86229 Ntsc Line 21 Ccd Decoder
• Manufacturer: ZiLOG Semiconductor

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OSD displays. Figure 5 illustrates the characters with a
drop-shadow added.
Extended Features
The EIA–608 specification has defined new extended fea-
tures such as optional Background and Foreground display
attributes and optional Extended Characters. The Z86229
always responds to the Extended Characters, but the Ex-
tended Background/Foreground response can be controlled
by the user. The Background and Foreground attributes add
codes for background colors, black and transparent fore-
ground, opaque, and semi-transparent backgrounds. The
BOX signal output pin is set to a tri-state condition when-
ever one of the semi-transparent attribute codes is active.
The external keying circuits can then use this condition to
implement the intended video display.
The font for the Extended Characters are illustrated in Fig-
ure 6. The accented capital letters have been implemented
by placing the accent marks above the character cell. When
selected, this mode results in the accent marks being written
into the character cell space of the row above. In some op-
erating modes, the Z86229 expands the size of the overall
box height by adding two additional scan lines at the top
and one additional line at the bottom. There is now room
for the accent marks in the topmost row and an added black
% Q P V K P W G F
line below the descenders of any lowercase characters in the
last row.
This approach is desirable because shrinking the capitals to
make room for the accent mark within the character cell
makes poor quality characters. In some cases, there would
be no differentiation between the capital and lower case let-
ter. Extended characters also have the advantage of mini-
mizing the ROM size and providing a good readable font
that closely matches what is normally seen in print.
In the unlikely case of a conflict between an accented capital
letter in one row and a lower case descender in the same
character position in the row above, the descender is given
priority. The improved readability of this approach over
shrunk capital letters far outweighs this potential conflict
and results in a cost-effective compromise for providing a
full, extended features implementation.
The Extended Characters share their address space with the
OSD Graphics Characters. When a BOX display is used,
the Extended Character set is in force; however, if a Drop
Shadow display is used, the Graphics Characters are in
force. For Caption and Text display modes, if the Drop
Shadow is set, the user must also command the Z86229 to
switch back to Extended Characters.
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