SAA5X9X Datasheet, PDF (36/68 Pages) NXP Semiconductors – Economy teletext and TV microcontrollers

Philips Semiconductors
Economy teletext and TV microcontrollers
Preliminary specification
SAA5x9x family
8.11 Wide Screen Signalling (SAA529xA and
SAA549x only)
The Wide Screen Signalling data transmitted on line 23
gives information on the aspect ratio and display position
of the transmitted picture, the position of subtitles and on
the camera/film mode. Some additional bits are reserved
for future use. A total of 14 data bits are transmitted.
All of the available data bits transmitted by the Wide
Screen Signalling signal are captured by the appropriate
device in the family and stored in SFRs WSS1, WSS2 and
WSS3. The bits are stored as groups of related bits and an
error flag is provided for each group to indicate when a
transmission error has been detected in one or more of the
bits in the group.
Wide screen signalling data is only acquired when the
TXT8.WSS ON bit is set.
The TXT8.WSS RECEIVED bit is set by the hardware
whenever wide screen signalling data is acquired. The flag
can be reset by writing a logic 0 into the SFR bit.
8.12 525-line world system teletext
As well as the 625-line teletext format described
previously, the family can acquire teletext in the 525-line
WST (World System Teletext) format.
The 525-line format is similar to the 625-line format but the
data rate is lower and there are less data bytes per packet
(32 rather than 40). There are still 40 characters per
display row so extra packets are sent each of which
contains the last 8 characters for four rows. These packets
can be identified by looking at the ‘tabulation bit’ (T), which
replaces one of the magazine bits in 525-line teletext.
When an ordinary packet with T = 1 is received, the
decoder puts the data into the four rows starting with that
corresponding to the packet number, but with the 2 LSB’s
set to logic 0. For example, a packet 9 with T = 1 (packet
X/1/9) contains data for rows 8, 9, 10 and 11. The error
checking carried out on data from packets with T = 1
depends on the setting of the TXT1. 8 BIT bit and the error
checking control bits in the page request data and is the
same as that applied to the data written into the same
memory location in the 625-line format.
The rolling time display (the last 8 characters in row 0) is
taken from any packets X/1/1, 2 or 3 received. In parallel
magazine mode only packets in the correct magazine are
used for rolling time. Packet number X/1/0 is ignored.
The tabulation bit is also used with extension packets.
The first 8 data bytes of packet X/1/24 are used to extend
the Fastext prompt row to 40 characters. These characters
are written into whichever part of the memory the
packet 24 is being written into (determined by the ‘X24
Posn’ bit).
Packets X/0/27/0 contain 5 Fastext page links and the link
control byte and are captured, Hamming checked and
stored by in the same way as are packets X/27/0 in
625-line text. Packets X/1/27/0 are not captured.
Because there are only 2 magazine bits in 525-line text,
packets with the magazine bits all set to a logic 0 are
referred to as being in magazine 4. Therefore, the
broadcast service data packet is packet 4/30, rather than
packet 8/30. As in 625 line text, the first 20 bytes of packet
4/30 contain encoded data which is decoded in the same
way as that in packet 8/30. The last 12 bytes of the packet
contains half of the parity encoded status message.
Packet 4/0/30 contains the first half of the message and
packet 4/1/30 contains the second half. The last 4 bytes of
the message are not written into memory. The first
20 bytes of the each version of the packet are the same so
they are stored whenever either version of the packet is
acquired.
In 525-line text each packet 26 only contains ten 24/18
Hamming encoded data triplets, rather than the 13 found
in 625-line text. The tabulation bit is used as an extra bit
(the MSB) of the designation code, allowing 32 packet 26s
to be transmitted for each page. The last byte of each
packet 26 is ignored.
The device automatically detects whether 525 or 625-line
teletext is being received by checking whether teletext
packets are being recognised, and switching to the other
system if they aren’t.
The TXT13.625 TXT bit is set if the device has decided,
using the algorithm above, that 625-line text is being
received. The TXT13.525 Text bit is set if the device has
decided that 525-line text is being received. If the device
has not decided which type of text is being received then
neither flag is set.
The ‘FORCE ACQ0’ and ‘FORCE ACQ1’ bits in TXT17
can be used to override the automatic detection and
selection mechanism; see Table 17.
1997 Jul 07
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