SAA5X9X Datasheet, PDF (27/68 Pages) NXP Semiconductors – Economy teletext and TV microcontrollers

Philips Semiconductors
Economy teletext and TV microcontrollers
Preliminary specification
SAA5x9x family
Table 13 Notation used in Table 12
MNEMONIC
MAG
PT
PU
HT
HU
MT
MU
E
DESCRIPTION
Magazine
Page Tens
Page Units
Hours Tens
Hours Units
Minutes Tens
Minutes Units
Error check mode
8.4 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
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 alphanumeric
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.
8.5 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 uncorrectable 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 uncorrectable errors are detected in
any other Hamming checked data the byte is not written
into the memory.
1997 Jul 07
27