eprom failure modes

F

Fritz Oppliger

Guest
I came across a new one today:
eprom (27c512) programs fine,
verifies fine,
runs like crap. lots of errors.
Same code in an emulator runs fine.
Same code read back into the programmer and verified again fine.
Same code in another physical 27c512 chip runs fine (same target board).
What could the chip be doing differently when plugged into the target
board vs. the programmer?
 
Try verifying with slight variations in the supply voltages. Also see if
it's giving you good logic-level voltages on the outputs.

"Fritz Oppliger" <fritzo_two_@direcway.com> wrote in message
news:eek:pscuohbmvkwe1hx@free.teranews.com...
I came across a new one today:
eprom (27c512) programs fine,
verifies fine,
runs like crap. lots of errors.
Same code in an emulator runs fine.
Same code read back into the programmer and verified again fine.
Same code in another physical 27c512 chip runs fine (same target board).
What could the chip be doing differently when plugged into the target
board vs. the programmer?
Click to expand...
 
Fritz Oppliger wrote:
I came across a new one today:
eprom (27c512) programs fine,
verifies fine,
runs like crap. lots of errors.
Same code in an emulator runs fine.
Same code read back into the programmer and verified again fine.
Same code in another physical 27c512 chip runs fine (same target board).
What could the chip be doing differently when plugged into the target
board vs. the programmer?
Click to expand...
Is this one of those chips that have a window for erasure?
Is light shining on the chip?
--
John Popelish
 
On Mon, 16 Aug 2004 17:18:37 -0700, "Fritz Oppliger" <fritzo_two_@direcway.com>
wrote:

eprom (27c512) programs fine,
verifies fine,
runs like crap. lots of errors.
Same code in an emulator runs fine.
Same code read back into the programmer and verified again fine.
Same code in another physical 27c512 chip runs fine (same target board).
What could the chip be doing differently when plugged into the target
board vs. the programmer?
Click to expand...
Assuming your board is designed well, just throw the darned thing away. They
are cheap to replace.

Jon
 
On Mon, 16 Aug 2004 17:18:37 -0700, "Fritz Oppliger"
<fritzo_two_@direcway.com> wrote:

I came across a new one today:
eprom (27c512) programs fine,
verifies fine,
runs like crap. lots of errors.
Same code in an emulator runs fine.
Same code read back into the programmer and verified again fine.
Same code in another physical 27c512 chip runs fine (same target board).
What could the chip be doing differently when plugged into the target
board vs. the programmer?
Click to expand...
Could be slow access time.

John
 
On Mon, 16 Aug 2004 20:36:21 -0400, John Popelish <jpopelish@rica.net>
wrote:

Fritz Oppliger wrote:

I came across a new one today:
eprom (27c512) programs fine,
verifies fine,
runs like crap. lots of errors.
Same code in an emulator runs fine.
Same code read back into the programmer and verified again fine.
Same code in another physical 27c512 chip runs fine (same target board).
What could the chip be doing differently when plugged into the target
board vs. the programmer?

Is this one of those chips that have a window for erasure?
Is light shining on the chip?
Click to expand...
Yes, UV erasable, with window. But there really is not much light in here.
There is a plain white paper label stuck on the window, proudly
proclaiming the version number I gave it.
I have done many hundreds of Eproms but so far they either worked or
failed to program/ verify.
I'll chalk this one up to some subtle (ESD?) degradation that affects its
speed.
And I may throw it away. Or I may keep it for some future forensic need
(with all the other stuff awaiting the same unlikely day...)

Are you suggesting trying it out with a light-impermeable label on it?
I can try that.
 
Subject: eprom failure modes
From: "Fritz Oppliger" fritzo_two_@direcway.com
Date: 8/16/2004 7:18 PM Central Daylight Time
Message-id: <opscuohbmvkwe1hx@free.teranews.com


I came across a new one today:
eprom (27c512) programs fine,
verifies fine,
runs like crap. lots of errors.
Same code in an emulator runs fine.
Same code read back into the programmer and verified again fine.
Same code in another physical 27c512 chip runs fine (same target board).
What could the chip be doing differently when plugged into the target
board vs. the programmer?
Click to expand...
Hi, Fritz. First look at the numbers after the 27C512. You might find
something like -15 (meaning 150 ns access time). If the number is different on
the two ICs you have, that would be the primary suspect. If the numbers are
the same, look at replacing with a faster access time 27C512. If the design is
right on the edge with data access times, one IC could work and another not,
but both of them meet the spec. This is the type of problem that requires
muscling through all the data sheets for worst case specs on processor, glue
logic if present, and EPROM on memory reads, then doing the maths. Not easy,
but there it is. You'd be astounded, but sometimes engineers spec memory chips
based on typical times and crossed fingers rather than worst-case. If that
solves the problem, you're good to go. Also look to see if one IC in the
CPU-to-memory chain has been replaced by another possibly slower one on the
board.

If none of these work, it could just be a defective EPROM.

Good luck
Chris
 
In article <2qp2i01batnet05aj41o037ggdq2ogdh85@4ax.com>,
jjlarkin@highlandSNIPtechTHISnologyPLEASE.com says...
On Mon, 16 Aug 2004 17:18:37 -0700, "Fritz Oppliger"
fritzo_two_@direcway.com> wrote:


I came across a new one today:
eprom (27c512) programs fine,
verifies fine,
runs like crap. lots of errors.
Same code in an emulator runs fine.
Same code read back into the programmer and verified again fine.
Same code in another physical 27c512 chip runs fine (same target board).
What could the chip be doing differently when plugged into the target
board vs. the programmer?

Could be slow access time.

John



I'm voting for this explaination. I have had it happen in the past. I
Click to expand...
have yet to see a programmer that actually tests the part ANYWHERE near
the speed the part should be capable of. The programmer is probably
operating in the high microseconds not nanoseconds.

Jim
 
Fritz Oppliger wrote:
On Mon, 16 Aug 2004 20:36:21 -0400, John Popelish <jpopelish@rica.net
wrote:

Fritz Oppliger wrote:

I came across a new one today:
eprom (27c512) programs fine,
verifies fine,
runs like crap. lots of errors.
Same code in an emulator runs fine.
Same code read back into the programmer and verified again fine.
Same code in another physical 27c512 chip runs fine (same target board).
What could the chip be doing differently when plugged into the target
board vs. the programmer?

Is this one of those chips that have a window for erasure?
Is light shining on the chip?

Yes, UV erasable, with window. But there really is not much light in here.
There is a plain white paper label stuck on the window, proudly
proclaiming the version number I gave it.
I have done many hundreds of Eproms but so far they either worked or
failed to program/ verify.
I'll chalk this one up to some subtle (ESD?) degradation that affects its
speed.
And I may throw it away. Or I may keep it for some future forensic need
(with all the other stuff awaiting the same unlikely day...)

Are you suggesting trying it out with a light-impermeable label on it?
I can try that.
Click to expand...
If you have a label over the window, then light is probably not the
problem.
But you should be aware that light definitely messes up the operation
of these devices, and they should be kept in dim light or darkness
during the programming and verification process, as well as when in
use.

--
John Popelish
 
"John Larkin" <jjlarkin@highlandSNIPtechTHISnologyPLEASE.com> wrote in
message news:2qp2i01batnet05aj41o037ggdq2ogdh85@4ax.com...
On Mon, 16 Aug 2004 17:18:37 -0700, "Fritz Oppliger"
fritzo_two_@direcway.com> wrote:


I came across a new one today:
eprom (27c512) programs fine,
verifies fine,
runs like crap. lots of errors.
Same code in an emulator runs fine.
Same code read back into the programmer and verified again fine.
Same code in another physical 27c512 chip runs fine (same target board).
What could the chip be doing differently when plugged into the target
board vs. the programmer?

Could be slow access time.

John
Click to expand...
Another possibility is that the part has been stressed with ESD or some
other operating condition. EPROM programmers do not run the part at full
speed so it may pass in the programmer and fail in the target. It sounds
like we're talking about a single EEPROM here - chuck it out!
 
my conclusion, my response. THanks

On Tue, 14 Sep 2004 23:38:10 GMT, Dana Raymond <what@ever.com> wrote:


What could the chip be doing differently when plugged into the target
board vs. the programmer?

possibility is that the part has been stressed with ESD or some
other operating condition. EPROM programmers do not run the part at full
speed so it may pass in the programmer and fail in the target. It sounds
like we're talking about a single EEPROM here - chuck it out!


EPROM.
Click to expand...
clunk.



--
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