6 May
2002
6 May
'02
12:52 p.m.
This stuff's already been corrected, and the only thing with which I'd take
issue is your assertion that it's WRONG, since I said precisely the same thing
you said. It's been a long time since I looked at an 8708 or its spec's, and
I was just remembering what I thought I recalled from a trigger instantiated
by seeing the "it's a 5-volt world" slogan on that brocheure. It's
been
firmly established, though not by me, but I believe it, that the 8708 is just
another 2708.
Dick
----- Original Message -----
From: "ajp166" <ajp166(a)bellatlantic.net>
To: <classiccmp(a)classiccmp.org>
Sent: Monday, May 06, 2002 6:00 PM
Subject: Re: 2708 Programming Algorithm?
That was, exactly, my point, Allison.
>> 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".
Maybe so, but I didn't listen. By the time it mattered, the 5-volt parts were
readily available.
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