Black Box RGB/EGA/CGA/MDA to DVI(/VGA) Converter, Руководство пользователя, Страница: 12 / 57

RGB/EGA/CGA/MDA TO DVI(/VGA) CONVERTER
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2. Overview
2.1 Introduction
VGA is the most familiar of the various graphics data standards or protocols for connecting a
display (monitor or flat screen) to a graphic source. For many years, computers have
generally connected to a display through a VGA interface. However, with the increased
popularity of TFT flat screens, a new standard has been developed: DVI. In DVI, graphic data
is transmitted digitally; VGA is an analogue standard.
Over the years, other analogue standards have also found popularity: CGA, EGA, MDA
(=TTL) and also RGB. An RGB Video transmission consists of R (red), G (green) and B
(blue) signals at a level of 0.7Vpp. The Green signal also carries the (composite)
synchronisation signals.
A screen designed for VGA cannot normally display RGB/TTL signals for two reasons:
- A VGA screen requires H/V-Synchronization as TTL signals
- Many RGB/TTL sources generate HSYNC frequencies below of 30kHz –
to slow for modern VGA displays.
With TFT screens, there is an additional problem: the incoming video signal has to be
digitised. Horizontal and vertical resolutions are normally selected from an internal table with
several, common, video modes. Unusual resolutions, often generated by older RGB graphic
sources cannot be detected.
To display RGB/TTL data on a modern VGA or DVI display, the RGB to DVI(/VGA)
Converter digitises the incoming signals, stores them in an internal video memory and
displays them from there in a common resolution. The picture can be displayed in original
size or format filling. The RGB to DVI(/VGA) Converter is equipped with various automatic
and manual video correction tools in an on screen utility (see page 25).