Re: Another idea for outputting to VGA/DVI/HDMI

[Michael J. Mahon <mjmahon@aol.com>]

Charlie <charlieDOTd@verEYEzon.net> wrote:
> On 3/23/2013 7:01 PM, Sheldon Simms wrote:
>> On 2013-03-23 20:53:33 +0000, Charlie said:
>>> 
>>> The problem with any card that uses data from the slot bus is the
>>> inability to synchronize with the Apple video output. This is the way
>>> the Carte Blanche works and I'm pretty sure the Second-Sight card
>>> worked in a similar way (although I've never seen one). The Carte
>>> Blanche output visually is quite good although it doesn't have the
>>> NTSC look. This works well with most video but because of the lack of
>>> synchronization, programs that rely on timing with Vertical Blanking
>>> or interrupting to change palettes, modes, etc. don't do well.
>>> 
>>> By the way sampling the bus doesn't have to be that fast. The Carte
>>> Blanche does it a 50MHz.
>> 
>> 50 Mhz is plenty fast enough, I was just wondering whether the
>> Beaglebone can do it that fast.
> 
> I agree, you probably only need to sample it faster than the Apple writes
> it which, of course, is much slower.
> 
>> Video sync is a solvable problem. Either take the signal where it is
>> available (IIe slot 7, etc.)
> 
> That would probably work with a //e but unfortunately not with a IIgs
> because the M2B0 signal is needed for the SHR graphics modes and M2B0 is
> not available on slot 7 (and the pin used for it in the other slots is used by CREF).
> I may try my hand at soldering a wire to connect the Sync signal to the
> Carte Blanche slot just to see how it works.  I can't picture many people
> wanting to do this though.

But all Apple II graphics modes use the same VBL signal, don't they?

-michael - NadaNet 3.1 and AppleCrate II: http://home.comcast.net/~mjmahon