[Open-graphics] Sample VGA translation code, for nanocontroller

[Patrick McNamara]

Jared Putnam wrote:
> VGA video memory is arranged into four 64k banks, called planes.  When
> you read from video memory, (depending on the read mode) the card only
> gives you one value, it latches data on every active plane.  There's a
> four-bit bitmask that determines this.  When it writes memory, it
> writes from the latches to every active plane.  Most modes just leave
> the latches on one setting; I think only Mode X lets you take advantage
> of this, though.
>
>   
>

.....

>> Is the 80x25 screen laid out as a linear array of 2000 16-bit words?
>>     
>
> Yes, but there is more than one screen, and you can switch between
> them.
>
>
>
>   
Also, one of the memory banks (plane 2 IIRC) contains the font
definition for text modes.

Patrick M