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VGA Hardware: Difference between revisions
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{{In Progress}}
<div style="text-align: center; background-color: green; padding: 5px; margin-left: 30%; margin-right: 30%;">See discussion page before editing.</div>
The VGA is a complex piece of hardware. Even though its old, many modern graphics cards are compatible with it, including NVidia and ATI cards. This can make writing an VGA driver rather attractive. The amount of compatibility varies however, and do not ever assume a compatible card without proper hardware detection.
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=== Read/Write logic ===
The Read/Write Logic performs several operations on the written/read data, and a set of internal registers called the latches. Reading from video memory loads these latches with the value emitted by video memory. Write operations use the latches as an additional data source, apart from the data written from the host processor.
The read/write logic has several different operation modes. These can be chosen by setting the Graphics Mode register. The VGA has four write modes and 2 read modes, which can be set independently. By default, the VGA operates in read mode 0 and write mode 0 in such a fashion that all written data goes straight to memory, and read data from each plane is ORed together.
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