TDA935x Philips, TDA935x Datasheet - Page 37

• Manufacturer Part Number: TDA935x
• Description: TV Signal Processor-Teletext Decoder with Embedded u-Controller
• Manufacturer: Philips

Philips Semiconductors
Data Standards
The data and clock standards that can be recovered are
shown in Table 10 below:-
Table 10 Data Slicing Standards
Data Capture Timing
The Data Capture timing section uses the Synchronisation
information extracted from the CVBS signal to generate
the required Horizontal and Vertical reference timings.
The timing section automatically recognises and selects
the appropriate timings for either 625 (50Hz)
synchronisation or 525 (60Hz) synchronisation. A flag
TXT12.Video Signal Quality is set when the timing section
is locked correctly to the incoming CVBS signal. When
TXT12.Video Signal Quality is set another flag
TXT12.625/525 SYNC can be used to identify the
standard.
Acquisition
The acquisition sections extracts the relevant information
from the serial stream of data from the MulVIP and stores
it in memory.
625 WST A
The family is capable of acquiring 625-line and 525-line
World System Teletext. 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.
Making a page request
A page is requested by writing a series of bytes into the
TXT3.PRD<4:0> SFR which correspond to the number of
the page required. The bytes written into TXT3 are stored
in a RAM with an auto-incrementing address. The start
address for the RAM is set using the TXT2.SC<2:0> to
define which part of the page request is being written, and
TXT2.REQ<3:0> is used to define which of the 10 page
requests is being modified. If TXT2.REQ<3:0> is greater
2001 Jan 18
TV signal processor-Teletext decoder with
embedded -Controller
Data Standard
Closed Caption
625WST
525WST
WSS
VPS
CQUISITION
6.9375 MHz
5.7272 MHz
Clock Rate
500 KHz
5.0 MHz
5.0 MHz
37
than 09h, then data being written to TXT3 is ignored. Table
11 shows the contents of the page request RAM.
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.
f the 'Do Care' bit for part of the page number is set to 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 0 then
every subcode version of the page will be captured.
Table 11 The contents of the Page request RAM
Note: MAG = Magazine PT = Page Tens PU = Page Units
HT = Hours Tens HU = Hours Units
MT = Minutes Tens MU = Minutes Units E = Error check
mode
When the Hold bit is set to 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 a
later section (‘Error Checking’).
For a multi 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.
Rolling Headers and Time
When a new page has been requested it is conventional
for the decoder to turn the header row of the display green
Column
Start
0
1
2
3
4
5
6
7
Identification
Minutes Units
TDA935X/6X/8X PS/N2 series
Minutes Tens
Hours Units
Hours Tens
Error Mode
Page Units
Page Tens
Magazine
Byte
DO CARE
DO CARE
DO CARE
DO CARE
DO CARE
DO CARE
DO CARE
PRD<4>
x
Tentative Device Specification
PRD<3>
HOLD
MU3
HU3
PT3
PU3
x
x
x
PRD<2>
MAG2
MU2
HU2
MT2
PU2
PT2
x
x
PRD<1>
MAG1
MT1
MU1
PU1
HT1
HU1
PT1
E1
PRD<0>
MAG0
MU0
HU0
MT0
PT0
PU0
HT0
E0