Re: Apple IIgs' Super Res Locked Up?

["Bryan Parkoff" <nospam@nospam.com>]

"Rob Greene" <nospam-greener@charter.net> wrote in message 
news:Xns96BEAC21F8340greenercharternet@69.28.186.121...
> "Bryan Parkoff" <nospam@nospam.com> wrote in
> news:IwJPe.34$m56.20@newssvr24.news.prodigy.net:
>
>>     I would like to modify pixel data directly on $2000 through $9CFF
>>     on
>> bank $E1.  I typed, "C029: C0" to turn on Super Res and "C029:00" to
>> turn off Super Res.  I tried either, but it locked up.  The screen
>> switches to green and red rows.  I forced to reboot Apple IIgs.
>>     Do you have idea why it forbids me from doing $C029?  Do you know
>>     if
>> there is routine to turn on/off Super Res?
>>
>> Bryan Parkoff
>
> I asked this question a month or two ago - check in the archives for all
> the nitty-gritty details.
>
> As for the C029 switch, you need to OR the bits.  On my ROM 01 GS, the
> lower nibble has (IIRC) a value of 7.  Changing those values is not
> recommended (I got the same thing).
Rob,

    Thanks for the information.  If you attempt to do like this below.

LDA $#C0
STA $C029
RTS

    Apple IIgs would crash because it is done READ/WRITE.  Apple IIgs' 
Hardware Reference book says that it must be READ/MODIFY/WRITE to prevent 
crash.  I tried another routine below.

LDA $C029
ORA $#C0
STA $C029
RTS

    This routine above works because first instruction is READ, second 
instruction is MODIFY, and third instruction is WRITE.  You can use "AND 
$#3F" to turn off Super Resolution.
    Does it make sense?

Bryan Parkoff