Specifications

CA10 Course Notes
Sharp Electronics (UK) Limited
CE Technical Support Group Page 39
Video Processing
IC201 provides the majority of the signal processing functions and is controlled by the I C bus 1 line from
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the main system microprocessor, IC101. Video signal switching is carried out by IC401 which also
provides Y and C inputs to IC201. Teletext, RGB and on screen display information are also fed into
IC201, which then outputs these signals to the CRT drive amplifier, IC901.
Figure 37 : Video Switching circuit diagram
The diagram above shows the video circuit in detail. Note that all inputs are terminated with a 75R load
resistor to ensure correct impedance matching with the respective source. The SCART socket video
inputs are protected from over voltage by the 7.5V zener diodes.
IC401 is a C-MOS triple 2 input analogue multiplexing IC. This means that depending on the switching
signal applied to pins 9, 10 and 11 either pins 12 and 17 or 13 and 1 will be connected to pins 11 and 10
of IC201 respectively. IC201 is then controlled over the I C bus to take each input as a video source - as
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in the case of the front AV socket or RGB socket. In the case of S-VHS pin 13 of IC401 connects to pin
11 of IC201 and pin 1 to pin 10, IC201 is then instructed to processes these signals as S-VHS.