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Re: Apple II VGA Video Generator Card Project



Jorge Chamorro Bieling wrote:
<aiiadict@gmail.com> wrote:


Think about how long it will take an Apple to fill a 1.2MB

Too long.

Even if the 6502 is running at 50mhz, imagine the nightmare
of bankswitching out 64k chunks, then moving data from the
active memory into the video buffer...


There is a reason that higher resolutions
and color depths go with more powerful
processors (and with more RAM).

more powerful CPU = faster speed + more address lines. (and
more linear addressable RAM)

We can put 16 megabytes of RAM in an apple II using
AE bankswitch method (1 byte register selects which
64k block to present to the CPU.  256*64k= 16384k = 16megs)
but what a pain it is to deal with this!

Rich


It's not if you just want to have 132 colums and 128 rows of text.
Or you just want to be able to hplot 0,0 to 1150,980.
Then it's a BIG pain when you have to deal with this as a bitmap...

While the time to put a character in a buffer is constant regardless
of the frame buffer size, drawing a line is proportional to the size
of the frame buffer, so all line drawing will take longer.

That's why we have to think carefully about this things...

That's my point.  ;-)

Again, not an issue when simply "mirroring" the existing
modes, since all extra work is on the card.

-michael

Music synthesis for 8-bit Apple II's!
Home page:  http://members.aol.com/MJMahon/

"The wastebasket is our most important design
tool--and it is seriously underused."