Re: How does the apple2 RGB card work?

["Bryan Parkoff" <none@nospam.net>]

"General_Failure" <tristan.mumford@gmail.com> wrote in message 
1148655592.949145.227670@j55g2000cwa.googlegroups.com">news:1148655592.949145.227670@j55g2000cwa.googlegroups.com...
> swtownsend said:
>>Hello,
>
>>    I have a spare RGB monitor card for the IIe.  If you want one to
>>take apart and study, or just to put in your IIe and use, let me know.
>>swtownsend(at)hotmail.com
>
> Yes. Yes. Yes.
> For both study and use. I'll send you an e-mail.
> I've just been figuring out how to use gschem (So much neater than
> hand-drawn). I'd have no objections to doing a simple circuit trace and
> schematic for those who are interested.
> I'm going to be doing the same on a C64 Viatel adaptor I have in the
> near future too.
>
> Unlike Mr. Parkoff, unfortunately I don't have things like a CRO, but I
> can usually figure out the ins and outs of a circuit fairly quickly. I
> am very interested to see the results of his research though, because
> like I said, I don't have access to the equipment.
>
> Having a //e platinum can make ascertaining the 'big picture' a little
> difficult at times too because of the custom ICs.
>
> Bryan Parkoff said:
>>   Right now, he and I are working together to develop schematic.  After
>>the schematic is developed, he may be able to design aux controller card 
>>for
>>VGA monitor, but it is almost impossible to deal between 15.734K and 30K
>>horizontial freq.  DMA may be needed.
>
> Speaking from a nonspecialised viewpoint, I can't understand why these
> may be problematic.
> If you are talking about directly pumping data to the monitor, then
> yes, it is a problem. However, if all you want to do is perform an RGB
> encoded version of what is being displayed via the video out, it is a
> little simpler.
> CGA and EGA monitors run at ~15Khz horizontal refresh, as does the
> video out.
> What I am uncertain of is whether the memory reads for the video
> display are opaque to the expansion bus.
> If not, then listening to the reads performed should be sufficient to
> create the basis of a fully mirroring RGB device.
> The sync signals are another matter which I am unable to address
> currently.
>
> If the card were to cache the writes done to the video area of memory,
> it would render the card independent of the bus and allow custom
> refresh rates.
>
> Recently I have been considering the merits of interfacing an 8-bit VGA
> ISA bus card to other architectures. So far I have not come up with any
> reasons why it would not be possible.
> There is an upside and downside to doing this:
> -Upside-
> *Heaps of pretty colours
> *A second display
> *The use of modern monitors
> *Standard set of registers make VGA easily programmable
> *VGA cards have their own RAM, thus having near nil impact on system
> performance
>
> -Downside-
> *Custom written software would be needed
> *The adapter would be bulky
>
Hello,

    I want to make sure what I understand your view.  You want video modes 
(TEXT40/80, LORES40/80, and HIRES40/80) from aux/main memory to be mapped 
into video memory.  Then RGB card reads video memory and displays pixel by 
pixel to the screen.
    I do not think that 80 Col / RGB card have video memory.  It only runs 
at 1/14M or 70 ns to read NTSC pulse from aux or main memory.  NTSC pulse 
goes through the RGB circuit to translate into R, G, B, and I signal.  RGBI 
forms a pixel to the screen.  It is how 15.734K horizontial freq is 
manipulated from 14M.  I am not too sure if EGA is 15.734K.
    You ask about sync.  H sync and V sync are created through logical truth 
table from videocounter and H sync and V sync are combined into composition 
sync to the NTSC monitor.  RGB card receives C sync and separate it into H 
sync and V sync because most analog / digital monitors don't have C sync 
except Apple IIgs' analog RGB monitor.
    You can design a video card to create video memory which it allows to 
copy byte by byte from aux and main memory into video memory.  It will not 
depend on 14M, but it uses its own frequency to maniuplate VGA or higher 
resolution.
    Is it what you are referring?  It is what I am doing to capture video 
data from R, G, B, and I signal and also well with Apple IIgs' RGB signals.

Bryan Parkoff