Yeah, I was also thinking that the clock might present a snag; one way
to find out I guess. FWIW I've replaced clocked RAMs in a R-S M100 with 
an ordinary 62256, ignoring the clock signal, and that worked without any
glitches. Time to heat up the soldering iron I guess and maybe revive a
dead PET while I'm at it. 

Thanks for the chat and the PCB layout!

mike
*************************************************************************************


M H Stein wrote:
> Well, since Nicolas also says that the ROMs need decoding logic, I'm 
> almost certainly missing something; since I'm metaphorically from 
> Missouri I guess I'll have to cobble something together to see just what
> it is.
>   
I'm looking at this schematic:  
http://zimmers.net/anonftp/pub/cbm/schematics/computers/pet/2001/320008-2.gif

I think you're original idea would work, *assuming* pin 16 does not 
matter.  If the ROMS need to clear off the bus on PHI2 inactive and the 
SELECT lines don't handle that, then you'll have issues.

> BTW, what *do* I need to print those colour-on-black-background 
> schematics?
>   
They print fine for me here (they do print as black, though), but here's 
a white background version: 
http://www.jbrain.com/vicug/gallery/ROM-el/6540_ROM_el_schematic_001?full=1

> Hope I'm not wasting too much of your time,
>   
No, it was fun to lay it out, and I'm happy to run a batch, but I know 
this group likes to tinker, so I'm happy just uploading the images and 
the EAGLE files and moving on.


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