saa5290ps NXP Semiconductors, saa5290ps Datasheet - Page 41

• Manufacturer Part Number: saa5290ps
• Description: Economy Teletext And Tv Microcontrollers
• Manufacturer: NXP Semiconductors

Philips Semiconductors
9.7
When used with 525-line display syncs, the devices modify
their displays such that the bottom line is omitted from
each character cell. The character sets have been
designed to be readable under these circumstances and
anyone designing OSD symbols is advised to consider this
mode of operation.
9.8
Character codes 80H to 9FH are not addressed by the
teletext decoding hardware. An editor is available to allow
these characters to be redefined by the customer.
The alternative character shapes in columns 8a and 9a
(SAA549x only) can be displayed when the ‘graphics’
serial attribute is set. This increases the number of
customer definable characters to 64.
To ensure compatibility with devices only having 32 OSD
characters, the additional OSD characters are only
accessible when the TXT4.OSD BANK ENABLE bit is set.
If this bit is not set, the characters in columns 8 and 9 will
be displayed in both alphanumeric and graphics modes.
9.9
Character codes 00H to 1FH, B0H to B7H and
BCH to BFH are interpreted as control characters which
can be used to change the colour of the characters, the
background colour, the size of characters, and various
other features. All control characters are normally
displayed as spaces.
The alphanumerical colour control characters
(00H to 07H) are used to change colour of the characters
displayed.
The graphics control characters (10H to 17H) change the
colour of the characters and switch the display into a mode
where the codes in columns 2, 3, 6 and 7 of the character
table (see the character table above) are displayed as the
block mosaic characters in columns 2a, 3a, 6a and 7a.
The display of mosaics is switched off using one of the
alphanumerics colour control characters.
The ‘new background’ character (1DH) the background
colour of the display, sets the background colour equal to
the current foreground colour. The ‘black background’
character (1CH) changes the background colour to black
independently of the current foreground colour. The
background colour control characters in the upper half of
the code table (B0H to B7H) are additions to the normal
teletext control characters which allow the background
colour to be changed to any colour with a single control
1998 Dec 14
Economy teletext and TV microcontrollers
525-line operation
On-Screen Display characters
Control characters
41
character and independently of the foreground colour.
The background colour is changed from the position of the
background colour control character.
Displayable characters between a ‘flash’ (08H) and a
‘steady’ (09H) control character will flash on and off.
Displayable characters between a ‘conceal display’ (18H)
character and an alphanumerics or graphics control
character are displayed as spaces, unless the
TXT7.REVEAL bit is set.
The ‘contiguous graphics’ (19H) and ‘separated graphics’
(1AH) characters control the way in which mosaic shapes
are displayed. The difference between the two is shown in
Fig.12.
Control characters encountered between a ‘hold graphics’
(1EH) control character and a ‘release graphics’ (1FH)
control character are displayed as the last character
displayed in graphics mode, rather than as spaces. From
the hold graphics character until the first character
displayed in graphics mode the held character is a space.
The ‘start box’ (0BH) and ‘end box’ (0AH) characters are
used to define teletext boxes. Two start box characters are
required to begin a teletext box, with the box starting
between the 2 characters. The box ends after an end box
character has been encountered. The display can be set
up so that different display modes are invoked inside and
outside teletext boxes e.g. text inside boxes but TV
outside. This is described in Section 9.13.
The ‘normal size’ (0CH), ‘double height’ (0DH), ‘double
width’ (0EH) and ‘double size’ (0FH) control characters are
used to change the size of the characters displayed. If any
double height (or double size) characters are displayed on
a row the whole of the next row is displayed as spaces.
Double height display is not possible on either row 23 or
row 24.
The character in the position occupied by the right hand
half of a double width (or double size) character is ignored,
unless it is a control character in which case it takes effect
on the next character displayed. This allows double width
to be used to produce a display in which blank spaces do
not appear when character attributes are changed.
The size implying OSD (BCH to BFH) control characters
are not standard teletext control characters and have been
included in this device to allow OSD messages to be
generated with the minimum disruption to the teletext page
stored in the memory. These characters are described in
full later in this document.
SAA5x9x family
Preliminary specification