Re: 6540 ROMs replacement ?

From: Nicolas Welte; address is valid for replies (Re:) only! (
Date: 2003-02-05 10:44:26

Hi Jürgen,

Jürgen Sievers wrote:
> But one of the 6540 may be really damage.  But what's the cause, why your
> adaptor doesn't work on the systems ROM but on the character generator?

The 6540 chip has five (!) chipselect inputs plus a Phi2 input. In the 
character ROM socket these are not used at all, so I don't support them, I 
simply leave the replacement EPROM enabled all the time. Works fine.

It was a bad habit at the time the PET was built to save decoding logic by 
applying address lines to these extra chipselect inputs. This way you could 
have an array of several ROM chips that would select themselves at the 
correct addresses. In a way these chips had their memory decoder built in 

There's also another reason why it won't work: My adaptor is so large that 
only one of them can be used in two adjacent sockets. Of course this could be 
fixed by putting an extra precision socket under every 2nd adaptor.

> When I look on the circuit diagram diagram I can see 2316B instead of 6540A.
> Maybe I have a wrong plan.

Check Funet, it has four different sets of schematics for the original 2001, 
you need the one that matches the ASSY NO. of your board.

> Do you have a prefabricated constructed one for me ?

Yes, please have a look at my order page:


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