saa5290 NXP Semiconductors, saa5290 Datasheet - Page 27

• Manufacturer Part Number: saa5290
• Description: Page Economy Teletext/tv Microcontroller
• Manufacturer: NXP Semiconductors

Philips Semiconductors
Display
The capabilities of the display are based on the
requirements of level 1 teletext, with some enhancements
for use with locally generated On-Screen Displays (OSD).
The display consists of 25 rows each of 40 characters,
with the characters displayed being those from
Rows 0 to 24 of the basic page memory. The page
memory stores 8-bit character codes which correspond to
260 displayable characters and 44 control codes, normally
displayed as spaces. Each character is defined by a matrix
12 pixels high and 10 pixels deep. When displayed each
pixel is 0.5 s wide and 1 TV line, in each field, high.
The SAA5290 signals the TV display circuits to display the
RGB outputs of the SAA5290 rather than video picture by
setting VDS HIGH. The way in which this signal is switched
is controlled by the TXT5 and TXT6 SFRs. There are three
control functions: background on, text on and picture on.
There are separate bits for each function for inside and
outside teletext boxes and if the newsflash or subtitle bits
are set. This allows the software to configure the type of
display required. The effect of the combination of these
bits is given in Table 16. The COR bits in Register 5 and
Register 6 control when the output is pulled LOW. This
output is intended to act on the TV display circuits to
reduce the contrast of the video display.
Table 16 Display mode
Display timing
The display circuitry is driven from the H/VSYNC inputs,
and is independent of the input video signal. Consequently
HSYNC and VSYNC are always required to slave
synchronize the display.
The FRAME output of the SAA5290 is provided to facilitate
de-interlacing the teletext display. The behaviour of
FRAME is controlled via the register bits
TXT0.DISABLE FRAME, TXT0.AUTO FRAME and
TXT1.FIELD POLARITY. If the active edge of VSYNC
occurs in the first half of a TV line then the field is even, and
February 1995
One page Economy Teletext/TV
microcontroller
PICTURE ON
0
0
0
1
1
1
TEXT ON
0
1
1
0
1
1
BACKGROUND ON
X
X
0
1
0
1
27
The display character set is given in Fig.9. The character
set provided contains all the characters required to display
Eastern and Western European languages. Register bit
TXT4.EAST/ WEST sets whether Eastern or Western
languages are set with the C12 to C14 bits. In order to
make on-screen displays easy to use, the SAA5290
contains additional display attributes in Column 11.
Control codes are categorized as ‘set at’ or ‘set after’.
‘Set at’ means the code has effect at the current character
position and ‘set after’ means they have effect from the
following character. Codes 11/0 to 11/7 are always
‘set at’. Codes 11/11 to 11/15 are ‘set after’ when defining
the start of an OSD box and ‘set at’ when ending an OSD
box. Codes 11/12 to 11/15 force a box condition allowing
on-screen display messages to be displayed without
having to erase the whole contents of the teletext page.
On-screen displays are only available in TV mode and not
in text mode. In mixed text and TV mode the displayed
screen is not defined if an OSD box is encountered in the
page memory.
if the active edge of VSYNC is in the second half of a line
then the field is odd. The active edge is controlled with
TXT1.V POLARITY. With TXT0.AUTO FRAME LOW
FRAME is HIGH for an odd field and LOW for an even
field. With TXT0.AUTO FRAME HIGH FRAME is only
active when text is being displayed, when video is
displayed it is forced LOW. When TXT0.DISABLE FRAME
is HIGH FRAME is always LOW. If
TXT1.FIELD POLARITY is logic 1 then VSYNC is delayed
by 32 s before being applied to the display timing circuits.
text mode, black screen
text mode, background always black
text mode
TV mode
mixed mode and TV mode
text mode, TV picture outside text area
RESULT
Preliminary specification
SAA5290