Programming 2708's

[Randy McLaughlin]

From: "Dwight K. Elvey" <dwight.elvey at amd.com>
Sent: Tuesday, June 28, 2005 5:26 PM

> >From: "Randy McLaughlin" <cctalk at randy482.com>
> >
> ---snip---
> >Intel changed the specifications of the 2708 a couple of times, later
docs
> >state it does not require programming from address 0.
> >
> >I have changed individual bits (only from a high to low, to go from low
to
> >high the entire chip must be erased).
> >
> >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
> >many bytes and I used it to modify previously written EPROM's.  The
buffer
> >in RAM was sequentially read but the writing was NOT sequential it would
> >skip bytes when a write was not needed.
> >
> >Any byte can have high bits changed to low even if they were previously
> >programmed.
> >
>
> Hi Randy
>  I recall the primary reason they wanted one to go through
> the entire cycle was that it gave the particular spot
> that was programmed a chance to cool down. I'm not sure if this
> was actually a real problem or just a suspected problem.
> I may have been an electrical issue with space charge as well.
>  Technically, you could skip locations that didn't need
> programming but you should insert a delay equal to the
> normal total time before programming the same location
> again.
>  Anyway, that is what I remember.
> Dwight

Unless you are writing just a few bytes skipping sections doesn't matter.

If for instance you are modifying all 8 bits of one byte and cycle over it
too much it will destroy the chip.  Writing 50 or more bytes where you are
modifying an average of 4 bits per byte would not give a problem.  Please
note writing a 1 to a bit does nothing and on average only 1/2 of the bits
are changed from a 1 to a 0.

I've programmed hundreds of 2708's and have had few problems.  The few
problems I've had have usually been that the EPROM would not erase to all
1's (bad chips).

I have destroyed a couple of 2708's by trying to modify a single byte too
rapidly but I saw it as a learning experience.  Since then I learned it is
possible to program a chip rapidly, safely, and reliably.

Randy
www.s100-manuals.com