
On-Screen Display Module (OSD)
Overview
MC68HC908TV24 — Rev. 2.1
Advance Information
Freescale Semiconductor
On-Screen Display Module (OSD)
227
17.4.4 OSD Output Logic
Programmable character attributes include color (foreground and
background), rounding, black outline, 3D shadow (OSD mode only),
blinking, underlining and italics (both in CC mode only). Rounding and
outline dots are half the width and length of the basic ROM character
pixel. In the vertical dimension, each pixel of the character matrix is
formed by a pair of odd and even lines of different interlace fields. To
produce the half-pixel rounding dot, the spatial displacement of odd and
even fields of the interlaced video is used, so that just one of the fields
displays the rounding or outline dot. The odd/even field indicator is
extracted by the closed-caption data slicer, which must be enabled to
provide field information to the OSD.
These attributes have a default set on a row basis, and many of them
can be modified inside the row by control characters. The CC mode and
the OSD mode have different character control codes and the display
behavior is different for each mode. In CC mode, all mid-row control
characters are displayed as background color spaces, whereas in OSD
mode, up to two control characters can be placed together without being
displayed. In OSD mode it is also possible to backspace a character and
display it on top of the preceding one, allowing the use of more than one
foreground color in one character.
The pixel pattern data from the pixel ROM passes through circuitry which
adds the selected attributes of rounding, black outline, shadow, italics
and underline. The resulting signal passes through a color encoder and
is converted into R, G, B, I, and FBKG signals. In OSD mode, if a
backspace control code appears between two characters, the second
one is read at the same time as the first, and the two of them go in
parallel to the color encoder to form a composite character. In this case
it is possible to apply rounding, black outline and shadow only to the first
character. The second one is added with no attributes applied.