[A83] Re: lcd mem as ram
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[A83] Re: lcd mem as ram
At 12:27 2002-01-04, you wrote:
>Could this extra memory be used as an offscreen gfx-buffer for fast
>(hardware)
>scrolling?? (a bit like Mode-X on PC's)
>
>just wonderin'...
nope. the lcd driver only supports vertical hardware scroll. It does this
by having a register that says what line in the memory (on the lcd driver)
that is the first line.
it starts reading from this line, and reads on until the end of the ram,
then it wraps over and reads the top, until it has read 64 lines.
Because of this, if you change the offset, your screen image will "wrap
around" and come back at top (or bottom, depending on what way you scroll)
the register is called "z-address", and you change it by writing a value
between $40 and $7F to the lcd control port.
unfortunatly, there is no register for changing the x-offset, so horizontal
hardware scroll is not possible.
which is a bit of a shame, since horizontal scroll in software is the slow
one of the two.
///Olle
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