Specifications

CA10 Course Notes
Sharp Electronics (UK) Limited
CE Technical Support GroupPage 42
Teletext
Teletext processing is carried out within IC106 ( STV5346 ). This IC is a 28 pin dual in line flat pack that
contains all the normal fast text processing capabilities including a small page store and on screen display
generation.
Figure 39 : Teletext Processor Circuit
When the user selects the teletext function, IC101 instructs the teletext processor, via the I C bus 2 line,
2
to switch IC201 to the RGB input via pin 12 of IC106. Any RGB signals coming out of IC106 will now be
switched by IC201 to the CRT drive amplifier, IC901.
As the teletext encoded information is contained within the incoming video signal, it is necessary to ensure
that the teletext processor is supplied with a composite video input. This composite signal enters IC106
on pin 1 ( CVBS ). Decoding takes place within the IC, using the clock frequency of 13.873MHz generated
by X102.
On screen display
Graphics that appear on the screen during the various control functions ( Sound control, picture
adjustments, tuning settings, etc. ) are all generated within IC106 under control from the main system
processor. The information used to generate the characters themselves is contained within the EPROM,
IC105. This data is dependant upon the control codes programmed within the microprocessor, IC101 at
manufacture, i.e. language, receiver functions etc. Therefore the microprocessor is dependent on the
destination country. Note that if this information is corrupted, then the receiver may start up in the
incorrect language or have a corrupted character set. It is very unlikely that the EPROM, IC105 would fail
in this way.