From: Ruud Baltissen (
Date: 1998-09-18 21:11:04

Hallo Henry,

> > Does anyone know the what speed a eprom must be for it to work in the
> > > C64? I have two eproms that are 350 ns, and fail in my C64.
> > 
> > The slowest DRAMs I've seen in a C64 are 300 ns.
> > 
> > > They do okay in my VIC-20. Is it the speed? 
> > 
> > It shouldn't be, since (in the case of NTSC) both machines run at the same
> > clock speed.  But on the other hand, the VIC-20 has some buffer chips on
> > the bus that the C64 doesn't have.
> Maybe that is why they work okay in the VIC-20 and not in the C64.
> > But why don't you use a normal 2764 or 27128 EPROM?  The pinout is not
> > that much different.  BTW, does anyone know where one could buy nicely
> > built 2764->2364 adapter sockets?
> Yes, I could use the 28 pin eproms you mentioned above with a little work,
> but I wanted to do a easy replacement of the 24 pin type. 

I've used 350 ns in the '80 WO problems. What the problem can be is that EPROMs 
sometimes "age", get slower. My Junior did not want to run at 1 MHz with a 250 
ns (!) 2764 but did on 500 KHz. A new one of 350 ns worked fine. 
I advise you to make the adapter. In this way you can use up to the 27512 ie. 8 
Kernals in 1 EPROM.

Groetjes, Ruud

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