Re: Apple][VGA - finally available

["Ferdinan Meyer-hermann" <ferdinan.meyer-hermann@a2central.com.remove-rw3-this>]

  To: Oracle
  Re: Re: Apple][VGA - finally available
  By: Oracle to comp.sys.apple2 on Thu Jul 03 2008 12:45 am

 > well done!
Thank you!
 > Why did you not add support for the IIGS?
Because this would require a completely different card. The ][, ][+, //c and
//e all have the same video circuitry, that generates 1-bit video (monochrome!)
that becomes colored because the NTSC TV interpretes some monchrome patterns as
color. So the card needs emulate this.
The //gs outputs 12-bit RGB video, and with four different timings (280,320,560
and 640 pixels per line) that require 12 times the memory (no problem) and
memory that is about 15 times faster (that _IS_ a problem). The RAM addressing
would need to be modified, too.
The color generation and it control logic would not be needed any more (which
is more than half the card!), but new control logic would be needed to handle
switching between the different GS video modes.
After all, there are two ICs left that would be used in both the //e and the
//gs. That's not much for a 23-chip design...
So you'll have to wait until someone designs a "GS2VGA"...
A real GS2VGA would also have the advantage of being cheaper and drawing less
power than a combined solution. And it is likely to cause less trouble


Regards,
Ferdinand Meyer-Hermann

PS: I'm gonna send a prototype to Henry Courbis from ReactiveMicro.com, who
will present it on KansasFest (I hope...)