Re: 6540 ROMs replacement ?

From: Nicolas Welte; address is valid for replies (Re:) only! (
Date: 2003-02-04 21:04:50

Jürgen Sievers wrote:
> Some pins a broken and after I have soldered a socket unter the ROMs they
> continue not in working condition. Some times aftyer power on the normal
> prompt appear but most some random is spread over the whole screen.

it seems you have a contact problem. I have the same in one of my PETs, and 
since I didn't want to install new sockets, I just put a precision socket 
under each ROM and plugged that into the original socket. It helped.

> My question is, is there a replacement for the 6540, maybe any EEPROM or
> PROMs type ?


> On the internet I had found some hints for an adaptor but I couldn't find
> the source or schema.

I have made a 6540 adaptor, but it is a simplified design that only works in 
the character ROM socket. I did this because the support of three (or even 
four?) chip select inputs would require an extra logic chip. If you look at 
the layout you will see that the 6540 pinout is very different from 25xx or 
27xx series EPROMs. The schematics (Eagle format) also show the pinouts of 
the 6540 and 6550.

For replacing all the system RAM and ROM I designed another circuit that 
plugs directly into the 6502 socket. You can read about both devices here:


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