TDA935x Philips, TDA935x Datasheet - Page 38

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

Philips Semiconductors
and to display each page header as it arrives until the
correct page has been found.
When a page request is changed (i.e.: when the TXT3
SFR is written to) a flag (PBLF) is written into bit 5, column
9, row 25 of the corresponding block of the page memory.
The state of the flag for each block is updated every TV
line, if it is set for the current display block, the acquisition
section writes all valid page headers which arrive into the
display block and automatically writes an alpha-numerics
green character into column 7 of row 0 of the display block
every TV line.
When a requested page header is acquired for the first
time, rows 1 to 23 of the relevant memory block are
cleared to space, i.e.: have 20h written into every column,
before the rest of the page arrives. Row 24 is also cleared
if the TXT0.X24 POSN bit is set. If the TXT1.EXT PKT OFF
bit is set the extension packets corresponding to the page
are also cleared.
The last 8 characters of the page header are used to
provide a time display and are always extracted from every
valid page header as it arrives and written into the display
block
The TXT0. DISABLE HEADER ROLL bit prevents any
data being written into row 0 of the page memory except
when a page is acquired off air i.e.: rolling headers and
time are not written into the memory. The TXT1.ACQ OFF
bit prevents any data being written into the memory by the
teletext acquisition section.
When a parallel magazine mode transmission is being
received only headers in the magazine of the page
requested are considered valid for the purposes of rolling
headers and time. Only one magazine is used even if don't
care magazine is requested. When a serial magazine
mode transmission is being received all page headers are
considered to be valid.
Error Checking
Before teletext packets are written into the page memory
they are error checked. The error checking carried out
depends on the packet number, the byte number, the error
check mode bits in the page request data and the TXT1.8
BIT bit.
If an incorrectable error occurs in one of the Hamming
checked addressing and control bytes in the page header
or in the Hamming checked bytes in packet 8/30, bit 4 of
the byte written into the memory is set, to act as an error
flag to the software. If incorrectable errors are detected in
any other Hamming checked data the byte is not written
into the memory.
Teletext Memory Organisation
The teletext memory is divided into 2 banks of 10 blocks.
Normally, when the TXT1.EXT PKT OFF bit is logic 0,
2001 Jan 18
TV signal processor-Teletext decoder with
embedded -Controller
38
each of blocks 0 to 8 contains a teletext page arranged in
the same way as the basic page memory of the page
device and block 9 contains extension packets. When the
TXT1.EXT PKT OFF bit is logic 1, no extension packets
are captured and block 9 of the memory is used to store
another page. The number of the memory block into which
a page is written corresponds to the page request number
which resulted in the capture of the page.
Packet 0, the page header, is split into 2 parts when it is
written into the text memory. The first 8 bytes of the header
contain control and addressing information. They are
Hamming decoded and written into columns 0 to 7 of row
25. Row 25 also contains the magazine number of the
acquired page and the PBLF flag but the last 14 bytes are
unused and may be used by the software, if necessary.
Row 25 Data Contents
The Hamming error flags are set if the on-board 8/4
Hamming checker detects that there has been an
incorrectable (2 bit) error in the associated byte. It is
possible for the page to still be acquired if some of the
page address information contains incorrectable errors if
that part of the page request was a 'don't care'. There is no
error flag for the magazine number as an incorrectable
error in this information prevents the page being acquired.
The interrupted sequence (C9) bit is automatically dealt
with by the acquisition section so that rolling headers do
not contain a discontinuity in the page number sequence.
The magazine serial (C11) bit indicates whether the
transmission is a serial or a parallel magazine
transmission. This affects the way the acquisition section
operates and is dealt with automatically.
The newsflash (C5), subtitle (C6), suppress header (C7),
inhibit display (C10) and language control (C12 to 14) bits
are dealt with automatically by the display section,
described below.
The update (C8) bit has no effect on the hardware. The
remaining 32 bytes of the page header are parity checked
and written into columns 8 to 39 of row 0. Bytes which pass
the parity check have the MSB set to 0 and are written into
the page memory. Bytes with parity errors are not written
into the memory.
Inventory Page
If the TXT0.INV on bit is 1, memory block 8 is used as an
inventory page. The inventory page consists of two tables,
- the Transmitted Page Table (TPT) and the subtitle page
table (SPT).
In each table, every possible combination of the page tens
and units digit, 00 to FFh, is represented by a byte. Each
bit of these bytes corresponds to a magazine number so
each page number, from 100 to 8FF, is represented by a
bit in the table.The bit for a particular page in the TPT is set
TDA935X/6X/8X PS/N2 series
Tentative Device Specification