SAA55XX Datasheet, PDF (53/84 Pages) NXP Semiconductors – TV microcontrollers with Closed Captioning (CC) and On-Screen Display (OSD)

Philips Semiconductors
TV microcontrollers with Closed Captioning (CC)
and On-Screen Display (OSD)
Preliminary specification
SAA55xx
18.5 Screen and global controls
A number of attributes are available that affect the whole
display region, and cannot be applied selectively to
regions of the display.
18.5.1 TV SCAN LINES PER ROW
The number of TV scan lines per field used for each
display row can be defined, the value is independent of the
character size being used. The number of lines can be
either 10, 13 or 16 per display row. The number of TV scan
lines per row is defined TXT21.DISP LINES<1:0>.
A value of 9 lines per row can be achieved if the display is
forced into 525-line display mode by
TXT17.FORCE DISP<1:0>, or if the device is in 10 line
mode and the automatic detection circuitry within display
finds 525-line display syncs.
18.5.2 CHARACTER MATRIX (H X V)
There are three different character matrices available,
these are 12 x 10, 12 x 13 and 12 x 16. The selection is
made using TXT21.CHAR SIZE<1:0> and is independent
of the number of display lines per row.
If the character matrix is less than the number of TV scan
lines per row then the matrix is padded with blank lines. If
the character matrix is greater than the number of TV scan
lines then the character is truncated.
18.5.3 DISPLAY MODES
CC: When attributes superimpose or boxing (see
Table 16, Serial Mode 0/1, bit 6) are set, the resulting
display depends on the setting of the following screen
control mode bits in the MMR Display Control.
TXT: The display mode is controlled by the bits in the
TXT5 and TXT6 registers. There are three control
functions - Text on, Background on and Picture on.
Separate sets of bits are used inside and outside teletext
boxes so that different display modes can be invoked.
TXT6 is used if the newsflash (C5) or subtitle (C6) bits in
row 25 of the basic page memory are set otherwise TXT5
is used. This allows the software to set up the type of
display required on newsflash and subtitle pages (e.g. text
inside boxes, TV picture outside) this will be invoked
without any further software intervention when such a
page is acquired.
When teletext box control characters are present in the
display page memory, the appropriate box control bit must
be set, TXT7.BOX ON 0, TXT7.BOX ON 1 − 23 or
TXT7.BOX ON 24. This allows the display mode to be
different inside the teletext box compared to outside.
These bits are present to allow boxes in certain areas of
the screen to be disabled. The use of teletext boxes for
OSD messages has been superseded in this device by the
OSD box concept, but these bits remain to allow teletext
boxes to be used, if required.
Table 17 Display modes
MOD 0 MOD 1 DISPLAY MODE
DESCRIPTION
0
0 Video
Disables all display activities, sets the RGB to true black and VDS to video.
1
0 Full Text
Displays screen colour at all locations not covered by character foreground
or background colour. The box attribute has no effect.
0
1 Mixed Screen Colour Displays screen colour at all locations not covered by character foreground,
within boxed areas or, background colour.
1
1 Mixed Video
Mixed Video mode displays video at all locations not covered by character
foreground, within boxed areas or, background colour.
Table 18 TXT display control bits
PICTURE ON
0
0
0
1
1
1
TEXT ON
0
1
1
0
1
1
BACKGROUND ON
EFFECT
X
Text mode, black screen
0
Text mode, background always black
1
Text mode
X
Video mode
0
Mixed text and TV mode
1
Text mode, TV picture outside text area
18.5.4 SCREEN COLOUR
2000 Feb 23
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