Hello all! I got some new schematics and data sheets from William Levak, and he also answered some questions about the PET schematics, see <URL:http://www.funet.fi/pub/cbm/schematics/computers/pet/answers.txt>. The attached question is not answered in that document. Marko ---------- Forwarded message ---------- Date: Wed, 13 May 1998 23:32:12 From: "William M. Levak" <firstname.lastname@example.org> To: Marko Mäkelä <email@example.com> Subject: Re: PET schematics bugs (fwd) I've checked the schematics and it does appear that $E900-EFFF should be available. I've looked at the memory on my 8032 and it looks like the space is available. The only thing left is to make up an EPROM with the screen editor in the lower half and see if it works. I'll try to do that in the next couple weeks. > From: Andre Fachat <firstname.lastname@example.org> > To: email@example.com > Subject: Re: PET schematics bugs > > > More on the PET I/O area size: > > The 8032 schematics have the ROM for $E*** labeled as a 2316, meaning > it being 2k. But they have BA11 still connected, and it is connected > to the /CS line as in the 2001N, so it is only selected when > /SELE is active ($E***) and A11 is low -> 2k ROM ($E000-$E7FF), no mirror. > > However, the 8032 PET mask /SELE for the ROM with x8xx, which is > active at addresses $*8**. This means the /SELE is _not_ active > in $E8**. > > So despite the labeling it should be possible to use a 4k ROM 2332, > which then has A11 at the rigth place and is selected at $E*** except > $E8**, et voila, 256 byte I/O space. > > So for 2k ROMs it should look like open-address space in $E900-$EFFF > and for 4k ROMs there is ROM in $E900-$EFFF - no further hardware > changes needed! > > This should also be an easy way to put in almost 2k of own code > into the ROM, without using $9*** and $A***. > > Only you should not use a 4k ROM with the SuperPET, as it uses the > $EFE0-$EFFF as I/O space and you then cannot read from there anymore > (bus conflict). > > Of course all this comes without warranty. > > so long > Andre
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