[Diy_efi] Re: looking for help with a prom N82S181

mbelloli at speedymotorsports.com mbelloli at speedymotorsports.com
Thu Nov 11 09:49:54 GMT 2004

Hello again,
     First in updating my website page, an error in the marking of traces
in my picture didn't get updated.  It is now fixed, and pin 18 is
correctly traced.  I really want to thank everyone for the input. 
Now I would just like to quickly respond to the question of using a
modern dvom in a cmos/ttl circuit for ohm readings.

(Ludis Langens wrote:)

> My instructions to Marcello are:  Pull out an ohm meter.  Find what

(phil hunter wrote:)
>NO!!! This is a good way to destroy ICs. Ohm meters have a voltage across
>the leads, this voltage can turn on internal diode junctions and the
>resulting "unlimited" current can destory devices anywhere along the trace.

     I'm guessing phil was talking about working on a live circuit.  In
that situation I would agree with Phil.  In an unpowered circuit, I
don't see the problem.  Yes a gate might be activated, but there is
no potential behind the gate to worry about.  So I'm going to say
both people are right depending on the whether the circuit is power
at the time.

     I never realized this was going to be as much a learning experience
as it has become.    In trying to understand the information that
Steve, and Ludis have provided I am truly wanting more than just
getting this thing working.  I want to understand it.  I have never
had the opportunity, nor the need to look at these signals before. 
Now that I have, my mind is never going to be at peace until I fully
understand exactly what is going on.

Pin 18 (/CE - chip enable on the 2716) held to 5v - I understand that one.
 And yes it is at 5volts always.  So pull this to ground instead. 
Enabling the chip.

Pin 19 (a10 on the 2716) which I was saying was noise - isn't is it?   Now
from what Steve was saying, and please correct me if I am wrong, is that
only half of the signal is usable?  When at Vcc ok, but when at Gnd I am
going to have a problem when hooked to a 2716 eprom.  So only half of the
time this signal would be usable.  Is that what was being said?  So this
signal is of no use to me with the 2716.  Instead wire it to Vcc, or Gnd
depending on which bank I want all my reading to be done from.

Pin 20 (/oe - output enable on the 2716) Pass through unchanged.  Here I
have the correct signal to enable the output of data to the bus.  This is
my true enable signal.  It is good as it stands.  When pulled low, enables
the output phase of the 2716.

Pin 21 (Vpp - programming power on the 2716)  Shouldn't go to ground, or
be toggled on the   2716.  Pull to 5v and that should be all that is
necessary at this pin.  We're not programming.

     I'm I getting this right?  Or do I need to be using that signal on
pin 19?  Can I not just pull pin 18 to ground enabling the chip
always, but not allow the output to be enabled except when pin 20 is
pulled to ground?  That would stop bus confliction wouldn't it?  I
still have a lot to learn.


Marcello A. Belloli

link to my page

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