SAA5500PS Philips Semiconductors, SAA5500PS Datasheet - Page 58

• Manufacturer Part Number: SAA5500PS
• Description: Standard TV Microcontrollers with On-Screen Display(OSD)
• Manufacturer: Philips Semiconductors

Philips Semiconductors
19.5
A number of attributes are available that affect the whole
display region, and cannot be applied selectively to
regions of the display.
19.5.1
The display mode is controlled by the bits in the TXT5 and
TXT6. 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
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.
Table 17 TXT display control bits
1999 Oct 27
Standard TV microcontrollers with
On-Screen Display (OSD)
PICTURE ON
Screen and global controls
D
ISPLAY
0
0
0
1
1
1
M
ODES
TEXT ON
0
1
1
0
1
1
23 or
BACKGROUND ON
58
X
X
0
1
0
1
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superseded in this device by the OSD box concept, but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.
19.6
Screen colour is displayed from 10.5 to 62.5 ms after the
active edge of the HSYNC input and on TV lines 23 to 310
inclusive, for a 625-line display, and lines 17 to 260
inclusive for a 525-line display.
The register bits TXT17.SCREEN COL<2:0> can be used
to define a colour to be displayed in place of TV picture
and the black background colour. If the bits are all set to
zero, the screen colour is defined as ‘transparent’ and
TV picture and background colour are displayed as
normal. Otherwise the bits define CLUT entries 9 to 15.
19.7
The display is organised as a fixed size of 25 rows
(0 to 24) of 40 columns (0 to 39), This is the standard size
for teletext transmissions. The control data in row 25 is not
displayed but is used to configure the display page
correctly.
Screen colour
Text display control
Text mode, black screen
Text mode, background always black
Text mode
Video mode
Mixed text and TV mode
Text mode, TV picture outside text area
EFFECT
Preliminary specification
SAA55xx