Re: Apple II VGA Video Generator Card Project

[aiiadict@gmail.com]

I added a link to your site on mine
(http://rich12345.tripod.com)

If you design the card using programmable
logic, extra (non compatible) video modes
could be added at any time.

perhaps put a mechanical switch on the
card that connects the PROGRAM pins
of the logic device to the address/data
bus.  Re-Program the device (new program
loaded off disk), flip the switch (no slot addresses
taken by the card any longer), and you've
got new logic on your card..

I've been looking at VGA "drivers" in FPGA, and
it seems that it isn't difficult.  Stretching the pixels
to fit the screen would be a matter of changing
timing.  FPGA can handle the timing

lookup table for HGR:


for v=0  to 191
Get V address
bit=1
for H=0 to 279(+40)

get data at Vaddress,H
AND with BIT
display on screen (change timing to stretch pixels)
ROL BIT
if bit=8 then bit=1:next H
NEXT V

here is link to driving VGA with FPGA:

http://www.fpga4fun.com/PongGame.html

Rich