Re: PET 4032 rom dumps

From: Gerrit Heitsch <*gerrit_at_laosinh.s.bawue.de*> Date: Sun, 29 Dec 2019 18:11:33 +0100 Message-ID: <f15a0839-6057-7cea-3d6b-17ddd70409ec_at_laosinh.s.bawue.de> · gerrit_at_laosinh.s.bawue.de

On 12/29/19 3:41 PM, Andy Grady wrote:
> Frank
> 
> Both ROMS are installed on $9000 socket
> 
> The 4K ROM looks identical to the Command-O ROM. Initialise SYS 36864 (I 
> believe)
> 
> http://www.geocities.ws/davegostelow/PETroms/CmdOAd.jpg

Yes, that looks like the ROM we had in our CBM systems back in school. 
Start was SYS 36864 so the ROM needs to go into an EPROM (2532) in the 
socket for $9000

The one we used had a small copy protection though. There is an INC 
command that will write to some address in the ROM, it's easy enough to 
find in a disassembly. No problem with an EPROM, but if you have a 
battery backed up RAM there, the ROM will not run unless you disable 
writing to it. Replace that command with 3 NOPs and you're good.

  Gerrit