From: chitselb@gmail.com   
      
   On Thursday, August 10, 2017 at 8:08:57 PM UTC-4, Harry Potter wrote:   
   > On Thursday, August 10, 2017 at 3:48:55 PM UTC-4, chitselb wrote:   
   > > If you needed 141 bytes of zero page on a C-64, what addresses would you   
   use?  BASIC is switched out, Kernal is still switched in, so anything BASIC   
   uses can be reallocated.  Having it all be contiguous so I can go in and out   
   of BASIC is important    
   too.   
   > >    
   > > On a PET (4.0 ROM) I'm just using $00-$8C (everything below jiffy clock)   
   and there's a little ML routine ('aloha') to swap the half page in and out,   
   but I want to port PETTIL to the C=64   
   >    
   > On a C64, the BASIC ROM uses ZP addresses $02-$8F, but you can use kernal ZP   
   locations you don't need in your program.  For example, $83-$8B and $AE-$B6   
   are used for tape and RS232 and $F7-$FF are for RS232 and free space.  Does   
   this help?   
      
   It looks like what they did is put the memory mapping I/O port at $00-$01 and   
   moved everything up by two?  Does it still have the problem of occasionally   
   pooping on address $10 ? There are a couple of places in the PET ROM where   
   writes to $10 occur e.g.    
   B3D8 STA $10 , even though Raeto's "Programming the PET/CBM" book says no, it   
   is unused   
      
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