2708 Programming Algorithm?

From: ajp166 <ajp166_at_bellatlantic.net>
Date: Mon May 6 19:00:02 2002

>>> I just remember that all the 87xx parts, 8741, 8755, 8748/49, etc,
were all
>>> 5-volt parts. further, I'm not at all sure that the 8080 had
below-ground
>>> signal levels, since they were intended to be attached to bipolar
parts, e.g.
>>> 8212, etc, which would have been intolerant of that. What I've got
in my lap
>>> is the 8080A data, which may, actually be different, but IIRC, the
8080 needed
>>> the negative bias supply so it could swing to ground and the +12 so
it could
>>> swing to a reasonable high level. My only contact with the 8080 was
on boards
>>> made by Intel, and, while I poked around with a 'scope and other gear
from
>>> time to time, I don't recall ever finding an address, data, or
control signal
>>> that wasn't TTL compatible.


Wrong! the 8080 and 8080A had basically the same levels and drive. the
issue
of negitive voltages on the output is a red herring.

The 8708 accoring to the 1978 8048 manual is a THREE voltage part with
the exact pinout as 2708. It's of course an intel number to allow the
"kitting:
practice that intel did do back then... "FAE>>> ya gotta use 8xxx parts".

Now for a note, looking at the 1979 Intel component data book the 2708
is
listed and save for a faster programming method the 8708 is identical per
notation in the data book!

Recommended programming pusle width is .1 to 1 millisecond and the
programming loop should not program any location for more than a total
of 100mS. Though I remember programmin them using a 1ms pulse and
doing a read to see if it took, programming it 5 times more for over
program and looping till it took and moving on to next location. If a
location
took more than 90 hits is was flagged as bad. That seemed to get the
best life out of the parts according to my notes. FYI: over eraseing
them seemed to kill them too.

Programming voltage is nominal 26V pulsed! All other votages are static
(Vcc, Vdd and Vss) with *ce/we being driven as needed for read or write.


> That's not the point. The point is that the inputs and outputs are
TTL (0V/5V) level and not a negative voltage. FWIW IIRC even the 8008
had a fan out of more than one. I have the manual and can look if it
matters.


Correct it was 2 LS loads. And the old 4004 was ttl if used with the
correct supply
voltages -10 and +5 wich was typical of the PMOS logic.

Allison
Received on Mon May 06 2002 - 19:00:02 BST