SAA5290A Philips Semiconductors, SAA5290A Datasheet - Page 39

• Manufacturer Part Number: SAA5290A
• Description: Economy teletext and TV microcontrollers
• Manufacturer: Philips Semiconductors

Philips Semiconductors
Table 18 Page request RAM for IDS data
9
9.1
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.
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. If the
TXT7.STATUS ROW TOP bit is set row 24 is displayed at
the top of the screen, followed by row 0, but normally
memory rows are displayed in numerical order.
The teletext memory stores 8 bit character codes which
correspond to a number of displayable characters and
control characters, which are normally displayed as
spaces. The character set of the device is described in
more detail below.
9.2
Each character is defined by a matrix 12 pixels wide and
10 pixels high. When displayed, each pixel is
and 1 TV line, in each field, high.
9.3
In common with their predecessors, these devices store
teletext pages as a series of 8 bit character codes which
are interpreted as either control codes (to change colour,
invoke flashing etc.) or displayable characters. When the
control characters are excluded, this gives an addressable
set of 212 characters at any given time.
More characters than this were required to give the
language coverage required from the first version of the
device, so the TXT4.East/West bit was introduced to allow
the meanings of character codes D0H to FFH to be
changed, depending on where in Europe the device was to
be used.
This bit is still used with the other language variants,
although the name East/West may not make much sense.
1997 Jul 07
Economy teletext and TV microcontrollers
1 to 7
COL
THE DISPLAY
0
Introduction
Character matrix
East/West selection
BIT7
X
X
BIT6
X
X
BIT5
X
X
1
12
s wide
BIT4
39
X
X
9.4
The meanings of some character codes between 20H and
7FH depend on the C12 to C14 language control bits from
the teletext page header.
The interpretation of the C12 to C14 language control bits
is dependent on the East/West bit.
9.5
In many of the character sets, the ‘twist’ serial attribute
(code 1BH) can be used to switch to an alternate basic
character code table, e.g. to change from the Hebrew
alphabet to the Arabic alphabet on an Arab/Hebrew
device. For some national option languages the alternate
code table is the default, and a twist control character will
switch to the first code table.
The display hardware on the devices allows one language
to invoke the alternate code table by default when the
East/West register bit is a logic 0 and another when the bit
is a logic 1. In all of the character sets defined so far, the
language which invokes the alternate code table is the
same for either setting of the East/West bit.
9.6
In the character sets character codes 80H to 9FH are OSD
symbols not addressed by the teletext decoding hardware.
An editor is available to allow these characters to be
redefined by the customer.
The SAA549x allows another 32 OSD symbols. These are
selected using the ‘graphics’ serial attribute.
9.7
The devices have a readable register TXT12 which
contains a 5 bit identification code TXT12.ROM VER R4 to
TXT12.ROM VER R0 which is intended for use in
identifying which character set the device is using.
Data Ch 3
National option characters
The twist attribute
On Screen Display symbols
Language group identification
BIT3
X
Data Ch 2
BIT2
X
SAA5x9x family
Data Ch 1
Preliminary specification
BIT1
X
Data Ch 0
BIT0
X