SAA5X9X Datasheet, PDF (26/68 Pages) NXP Semiconductors – Economy teletext and TV microcontrollers

Philips Semiconductors
Economy teletext and TV microcontrollers
Preliminary specification
SAA5x9x family
8 TELETEXT DECODER
8.1 Data slicer
The data slicer extracts the digital teletext data from the
incoming analog waveform. This is performed by sampling
the CVBS waveform and processing the samples to
extract the teletext data and clock.
8.2 Acquisition timing
The acquisition timing is generated from a logic level
positive-going composite sync signal VCS. This signal is
generated by a sync separator circuit which adaptively
slices the sync pulses. The acquisition clocking and timing
are locked to the VCS signal using a digital
phase-locked-loop. The phase error in the acquisition
phase-locked-loop is detected by a signal quality circuit
which disables acquisition if poor signal quality is detected.
8.3 Teletext acquisition
This family is capable of acquiring 625-line and 525-line
World System Teletext see “World System Teletext and
Data Broadcasting System”. Teletext pages are identified
by seven numbers: magazine (page hundreds), page tens,
page units, hours tens, hours units, minutes tens and
minutes units. The last four digits, hours and minutes, are
known as the subcode, and were originally intended to be
time related, hence their names. A page is requested by
writing a series of bytes into the TXT3 SFR which
corresponds to the number of the page required.
The bytes written into TXT3 are put into a small RAM with
an auto-incrementing address. The start address for the
RAM is set using the TXT2 SFR. Table 12 shows the
contents of the page request RAM.
TXT2.REQ0 to TXT2.REQ3 determine which of the
10 page requests is being modified for a 10 page teletext
decoder. If TXT2.REQ is given a value greater than 09H,
then data written into TXT3 is ignored.
Up to 10 pages of teletext can be acquired on the 10 page
device, when TXT1.EXT PKT OFF is set to logic 1, and up
to 9 pages can be acquired when this bit is set to logic 0.
If the ‘DO CARE’ bit for part of the page number is set to a
logic 0 then that part of the page number is ignored when
the teletext decoder is deciding whether a page being
received off air should be stored or not. For example, if the
‘DO CARE’ bits for the 4 subcode digits are all set to
logic 0s then every subcode version of the page will be
captured.
When the HOLD bit is set to a logic 0 the teletext decoder
will not recognise any page as having the correct page
number and no pages will be captured. In addition to
providing the user requested hold function this bit should
be used to prevent the inadvertent capture of an unwanted
page when a new page request is being made. For
example, if the previous page request was for page 100
and this was being changed to page 234, it would be
possible to capture page 200 if this arrived after only the
requested magazine number had been changed.
The E1 and E0 bits control the error checking which should
be carried out on packets 1 to 23 when the page being
requested is captured. This is described in more detail in
Section 8.5.
For the ten page device, each packet can only be written
into one place in the teletext RAM so if a page matches
more than one of the page requests the data is written into
the area of memory corresponding to the lowest numbered
matching page request.
At power-up each page request defaults to any page, hold
on and error check Mode 0.
Table 12 The contents of the Page request RAM
START
COLUMN
PRD4
PRD3 PRD2 PRD1 PRD0
0
DO CARE HOLD MAG2 MAG1 MAG0
Magazine
1
DO CARE PT3 PT2 PT1 PT0
Page Tens
2
DO CARE PU3 PU2 PU1 PU0
Page Units
3
DO CARE X
X
HT1 HT0
Hours
Tens
4
DO CARE HU3 HU2 HU1 HU0
Hours
Units
5
DO CARE X
Minutes
Tens
MT2 MT1 MT0
6
DO CARE MU3 MU2 MU1 MU0
Minutes
Units
7
X
X
X
E1 E0
1997 Jul 07
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