Re: Apple SCSI card question/request

[dempson@actrix.gen.nz (David Empson)]

Dennis Jenkins <dennis@usb.com> wrote:

> David Wilson wrote:
> > 
> > Wayne Stewart <waynes@intergate.bc.ca> writes:
> > >I hope your burner can handle 27C128 EPROMS.
> > >While the Rev B was a 2764 EPROM. the Rev A & C were 27128
> > >EPROMS.
> > 
> > Thanks for that. I was wondering why I had a 16KB image of an Apple SCSI
> > card ROM. I thought I must have got one for the High Speed card.
> 
> That being said, I will check with my friend.  Does anyone know of a web
> site where I can obtain information on the 2764 and 27128?

The only difference between typical 2764/27C64 and 27128/27C128 EPROMs
is an unused pin (26) on the 2764 becomes an extra address line on the
27128.  There may be differences in programming voltages and algorithms,
depending on the manufacturer.

If you have a burner which can only program a 2764, you might be able to
burn a 27128 in two passes, by tying the extra address pin low or high
as appropriate.

(Going from a 27C128 to a 27C256 is more complex, because they replaced
the program enable input with another address signal.)