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Vertical Blanking Interval (VBI)

Definition - What does Vertical Blanking Interval (VBI) mean?

Vertical blanking interval is an interval of time between the last line of a given frame and the beginning of the next frame, during which the incoming data stream is not displayed on a CRT (cathode ray tube) screen. It is the time interval allowed for the analog TV electron gun beam to move from the bottom of the current frame to the top of the next one as it scans images. This requires the last 45 lines of each 525-line frame.

This term is also known as vertical interval or VBLANK.

Techopedia explains Vertical Blanking Interval (VBI)

Vertical blanking interval was present in analog TV, VGA, DVI and other broadcast signals. Modern digital equipment does not require VBI. However, new equipment must be designed to be compatible with broadcast standards of older equipment.

When using analog TV, the VBI can be used to send digital data, called datacasting. Types of data sent include various test signals, closed captions, teletext, time codes and other digital data.

The former 16-bit video game graphics used VBI. However, it had to process all graphics programming very rapidly to fit into this short time interval. Synchronizing game code became problematic for early video games such as Atari 2600. Blank scan lines appeared at the top and bottom of the screen as video game manufacturers tried to extend the time interval.

Today, the use of double buffering has made such techniques obsolete. By use of a back buffer, for storing the results of all drawing operations in RAM, graphics are prevented from appearing to flicker as images are quickly used from RAM. These images are prevented from appearing to tear as images are constantly redrawn by computer monitors.

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