参数资料
型号: P83C766
厂商: NXP Semiconductors N.V.
英文描述: Microcontrollers for PAL/SECAM TV with OSD and VST
中文描述: 微控制器对于PAL / SECAM电视的OSD和伟仕
文件页数: 62/92页
文件大小: 382K
代理商: P83C766
1999 Mar 10
62
Philips Semiconductors
Product specification
Microcontrollers for PAL/SECAM TV
with OSD and VST
P8xCx66 family
17.8
Character ROM
128 character fonts may be stored in ROM: 126 customer
selected character fonts plus two reserved codes (the
Carriage Return code and the Space code).
Each character font is stored in a 12
×
19 dot matrix in
character ROM. However, only elements in rows 1 to 18
can be selected as visible dots on the TV screen. Row 0 is
used only in the North-West shadowing sub-mode and the
Border shadowing sub-mode when two character cells are
to be combined in a vertical direction to formulate a new
pattern. If combination of character fonts is not required
then row 0 should be filled with zeros. An example of a bit
pattern stored in ROM is shown in Fig.40.
A software package that helps the customer design the
character fonts on the screen and that also generates the
bit pattern HEX files automatically, is available on request,
from local Philips sales organisations. The package is run
under the MS-DOS environment for IBM compatible PCs.
17.9
Character ROM organization
ROM is divided into two parts: OSDL and OSDH.
The address of OSDL is from 0000H to 0FFFH and the
address of OSDH is from 1000H to 1FFFH.
The organisation of the bit patterns stored in ROM and the
file format to submit to Philips for customized character
sets is shown in Fig.40. Regarding Fig.40 the following
points should be noted.
1.
Each character is structured using 38 bytes.
2.
Row 0 of each font is reserved for vertical combination
of two fonts. In vertical mergence row 0 holds the
same code as row 18 of the previous font.
3.
Binary 1 denotes visual dots.
4.
ROM data files are in Intel HEX format on a byte basis.
Each byte is structured high nibble followed by low
nibble.
5.
The unused bytes in ROM must be filled with FFH.
17.10 Combination of two or more font cells
Two (or more) character font cells may be combined in a
vertical or horizontal direction to create a new higher
resolution pattern.
The combination of two cells in a horizontal direction is
straight forward and presents no problems to the user.
All 4 background/shadowing sub-modes can be used.
However, the combination of two character font cells in a
vertical direction is more difficult and care must be taken
otherwise the new pattern may be created with gaps in its
shadowing.
Row 0 in the character ROM is for use in the North-West
shadowing and Border shadowing sub-modes. If either
of these sub-modes is selected when combining two
character cells in a vertical direction then row 0 must
contain the bit pattern of row 18 of the font above it
otherwise a broken dot in the shadow may occur.
17.11 More about North-West shadowing and Border
shadowing sub-modes
Some special care must be taken when designing the
character bit pattern if the character is intended to be used
in the North-West shadowing or Border shadowing
sub-mode.
North-West shadowing and Border shadowing
sub-modes are limited in the 18 display scan lines box
only in the vertical direction if the character in the next
row is not in North-West shadowing sub-mode
(otherwise as described in Section 17.10) if the shadow
of the last foreground bit pattern line is intended to be
seen as well. To get correct shadowing following the
character font then in:
– North-West shadowing: row 18 must be blank
– Border shadowing: row 1 and 18 must be blank.
North-West shadowing and Border shadowing
sub-modes are not limited to the 12 horizontal OSD
dots. Shadows of the previous font cell may cross over
the 12 dot boundary and appear in the next font cell.
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