At 11:11 AM 8/20/02 -0400, you wrote:

>Why do you want to do this?  Performing an instruction test on a single chip
>micro seems rather pointless to me.  Instruction tests used to be popular
>back when a computer was on a bunch of boards and there could be failurs
>inside the CPU.  The likelyhood of blowing an individual transistor inside
>the CPU of a single chip micro is vanishingly small.  When chips go bad, it
>is usually the I/O drivers, power related, or in the case of some PICs the
>flash could wear out.

It's a specific requirement of the standard- IOW, it's too late to argue
about the relative merits of it.

Considering the number of bad dies per wafer is significant, there is a
100% chance that some marginal ones will slip through and fail
later if your sample is large enough. For non-MIL spec chips, I don't think
they even visually look at the chip to see if anything is horribly wrong.

Since this standard is specifically for *safety critical* applications,
consumer (high) volume products could result in an unacceptable level of
personal injury or property damage. While I do agree with Olin that some of
the testing is on the diminishing returns end, the overhead required is minimal
and there will be some improvement in reliability (it's not like the complexity
introduces significant failure modes itself). The ROM check just
happens to be a problem with PICs, and few other architectures. Who knows,
maybe a Motorola or Intel employee on the committee pushed it forward. It's
hard to argue against something that takes minimal resources and can only help
reduce the number of deaths etc.

If the micro can't do anything that could cause a safety hazard, no matter
how nuts or paralyzed it goes, you *don't* need to meet this particular
standard.

Best regards.

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
9/11 United we Stand

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