Video switchers, also known as a Video Display controller (abbreviated to VDC) is essentially the key component of a video signal generator. This kind of vision mixer is used for generating a visual signal in computers, and in some Cases an audio signal too, although this is just a secondary function. The video switcher first made its appearance in our homes in the first types of home computers, such as the old Commodores and Spectrums, and is now an integral part of video signal generator logic.
A video mixer cannot work alone however, as it needs support from various other parts of the computer to work. For example, pixel data is stored in the computer??s RAM, while character fonts are held in the ROM. Therefore, the video switcher chip will usually be totally integrated into the main computer, and so users will be able to see the video RAM it gives in the CPUs memory map. It can also act as a co-processor that acts independently, although this is not usually the case.
The video switcher is generally available in three different formats. Video shifters are the most basic type of production shifter, and take care of the video timing signals. These obtain data one byte at a time from the CPU, and use synchronization signals to produce a video signal. The CTRC video switcher reads data directly from the computer??s RAM, and this is then outputted either through a ROM or directly. Far more complex are video interface controllers. This kind of video switcher supports sprites and video RAM which is dedicated towards color attributes, thus making extremely high-resolution images possible.
