Programming 2708's

[Randy McLaughlin]

From: "Tony Duell" <ard at p850ug1.demon.co.uk>
Sent: Monday, June 27, 2005 4:49 PM


> > Intel changed the specifications of the 2708 a couple of times, later
docs
> > state it does not require programming from address 0.
>
> But did they also change the design of the chip, I wonder. Later 2708s
> may be more forgiving as to the programming algorithm they'll accept.
>
> Since Intel were so definite about having to go through all locations in
> order n times in the data sheet I have, I would certainly want to do it
> that way. Other methods might well damage the chip or lead to poor data
> retention.
>
> >
> > I have changed individual bits (only from a high to low, to go from low
to
> > high the entire chip must be erased).
>
> You can change individual bits, sure. The data sheet tells you how to do
> that.
>
> You have to go through _all_ the locations. If a locations is to be
> unchanged, you program it again with its current contents (a special case
> of this is that if you want to leave a location totally unprogrammed
> after erasing the chip, you re-write it with 0xFF).
>
>
> >
> > The later docs still state sequential writing but no longer require
starting
> > at 0 but I have written non sequentially and can swear by that.  I wrote
a
> > program that verified before writing to speed up programming, this
skipped
>
> Oh, it probably worked. But I wouldn't recomend doing it. 2708s are
> getting harder to find, so I'd not want to risk damaging one. And I
> certainly don't want to have to trace a fault caused by an unreliable bit
> in an EPROM. I would follow the manfacturer's instructions...
>
> It reminds me af a friend who programmed 27128s with a single 1ms pulse
> per location. It seemed to work. They verified OK. And then a bit later
> on he got data-rot....
>
> -tony
As I stated you can not rely on a single read to verify the data is
recorded, once you get a verify you MUST give it another write cycle to
ensure data.

For the later docs for the 27128's it confirms this and adds that VCC should
be raised to 6v.

Randy
www.s100-manuals.com