Re: Super Hi Res Stuff

[jmk3@crux2.cit.cornell.edu (Jay Krell)]

>From: adri0001@student.tc.umn.edu (Wouldn't you like to know)
 
>I needed to clear out the super-hi-res screen before I did
>anything to it...the problem was that I was clearing out the SHR screen and
>then flipping the SHR screen on...this was causing ghost pixels to get lit up
>at the bottom of the screen but ONLY when I ran the program for the first time
>after launching into GNO.  I go to GNO from Prosel, run my program, and the
 
>This continued until someone told me that I needed to flip the SHR screen on
>first...then clear it.  I am doing that now and it's working.
 
The problem is that the SHR memory is not, in its normal state, a linear 32K
chunk. I don't know if it is even at $E1/2000. For the SHR memory to appear as
we all know it, a bit must be set in NEWVIDEO ($C029?)
 
Hardware Ref 2nd ed p. 90, bit 6
 
"If this bit is 0, the 128K memory map is the same as the Apple IIe. If this
bit is 1, the memory map is reconfigured for use with SHR graphics mode: The
video buffer becomes one contiguous, linear address space from $2000 to $9D00."
 
Setting bit 7 both turns on the display and linearizes it.
 
You should set bit 6, clear the screen, then set bit 7.
 
There is no toolbox command to toggle bit 6, so you'll have to do it yourself.
 
  --Jay, jay.krell@cornell.edu