Re: The next step after writing my own Apple ][ wedge for the /// is...

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

schmidtd wrote:
> On Oct 8, 2:20 pm, lyricalnan...@dosius.ath.cx (Steve Nickolas) wrote:
>
> > An Apple /// emulator!
>
> [...]
>
> > I'm going to play a little fast and loose with the TTY code as there's still
> > some stuff I don't know (for one, how do you reload a charset on this
> > thing?
>
>
> Hmmm, that might prove problematic if you don't know already. :-)
>
> Here's some relevant text from Jeppson's article:
> http://apple3.org/Documents/Magazines/AppleIIIBits.html
>
> The Character Set: $0C00..0FFF. At boot time the system character set
> is loaded from SOS.Driver and stored in these pages. Similarly, if you
> download another character set from a program by issuing a DControl
> call #16 or #17 to the console driver, the new set is also placed
> here. But these pages are not the active character set in current use
> by the video generator. This is merely a staging area. From these four
> pages the character set is further transferred to the video
> generator's storage area, wherever that is. It is not in addressable
> memory. Presumably the machine contains a 1K RAM chip dedicated for
> this purpose, analogous to the ROM chip beneath the Apple II keyboard
> that contains the character set for that machine. In any event, you
> can change the copy in $0C00..0FFF all you wish, but nothing happens.

So that suggests that there is some little dance to be done to
get the hardware character gererator SRAM loaded.  Maybe it's as
simple as hitting a softswitch...

Sounds like some reverse engineering of SOS.Driver is needed.

-michael

NadaNet and AppleCrate II: parallel computing for Apple II computers!
Home page: http://home.comcast.net/~mjmahon

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