ADVANCE INFORMATION
VCT 38xxA
Micronas
67
3.11.OSD Layer
Apart from the WST layer, there is an additional OSD
layer on chip. The OSD layer accesses the CPU mem-
ory via DMA to read text, display attributes, and char-
acter font information.
The color outputs of the OSD
layer can have higher priority than the WST layer out-
puts. Thus, it is possible to overlay the teletext display
with an additional layer for user guidance (see Fig. 3–
19).
Fig. 3–19:
Display layer
The OSD layer reads text strings addressed by a pro-
grammable text pointer. Codes smaller than 80h will
address the character font, codes greater or equal 80h
are interpreted as control codes to change color or
character set (see Table 3–14). After reading a control
code the OSD layer will do an additional read to get the
next character code.
OSD Layer
WST Layer
Full Screen Layer
Code
Function
Notes
01
Underline On
only for 13 scanlines/character
02
Underline Off
03
Flash On
04
Flash Off
05
Italics On
06
Italics Off
07
Transparent
layer becomes transparent
08
Shadow
layer becomes transparent and
contrast is reduced to 66%
0C
END
end of layer
0D
CR
end of text line
0E
7F
80
FF
ASCII Character
using font 1 or font 2
Control Code
Only one control code per character
is allowed. Depending on OSD
Mode, the control code defines
either color or character set.
Color
bit 0 = foreground color blue
bit 1 = foreground color green
bit 2 = foreground color red
bit 3 = background color blue
bit 4 = background color green
bit 5 = background color red
bit 6 = replace white by transparent
bit 7 = 1
Character Set
bit 0 = bit 7 of character code
bit 1 = bit 8 of character code
bit 2 = bit 9 of character code
bit 3 =
bit 4 =
bit 5 =
bit 6 = latching shift to character set
bit 7 = 1
Shaded attributes are default at start of each text line.