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On-Screen Display
Mascot V OSD display support 256 different fonts at size of 12x18, 256 fonts contain
128 fixed fonts that stored in internal ROM, other 128 programmable fonts stored in
internal SRAM. OSD also supports Overlay port interface and color look-up table with
4 color indices from external OSD and Opaque, Translucence, Transparent display.
Diagram listed below is the concept of how OSD retrieves and displays OSD Font.
See FIG3-6.
When OSD key is been pressed, firmware will detect the change and perform the
procedure, once firmware start "drawing" OSD, it will program the OSD code and
attribute to the OSD SRAM. Chip will look-up the OSD code then retrieve the character
font data that corresponding to the code and then display the character on LCD panel.
There are 320 memory spaces from 0 to 319 in SRAM. It is sequentially mapped to the
OSD frame started from the upper-right corner and goes horizontally to the upper-left
corner and then move to 2
by 0 9 in row, total is 32x10=320 characters.
Diagram listed below is the concept of how 24bit RGB OSD character been composed,
see FIG3-7 OSD Display Flow Chart. Each OSD character font data that read out from
ROM table will use the 4-bit foreground and 4-bit background color to determine its color.
Use this 4-bit color index to look-up the palette and select related 15bit RGB foreground
and background color. And added 3bit 0 to each R, G, and B channel then generate 24it
RGB color for the OSD character.
ViewSonic Corporation
FIG3-6 On-Screen Display
nd
row etc. Ended at left-bottom corner. OSD frame are divided
22
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