Microprocessor question

[geneguy]

Good reason to stay away from "independent" distributors - No
warranty, suspicious circumstances re how they get their product.
Stick with the "franchised" distributors. They get their parts
directly from manufacturers. They also receive full technical support
from manufacturers (as opposed to having to ask questions on Usenet)

 

[budgie]

Good reason to stay away from "independent" distributors - No
warranty, suspicious circumstances re how they get their product.
Stick with the "franchised" distributors. They get their parts
directly from manufacturers.

Not always the case. Here in down-under-land, Maxim (as one example, also
LinearTechnology) are officially distibuted by Arrow Electronics Australia,
AFAIK a wholly owned subsidiary of Arrow Electronics in the U.S. Arrow Aus
order through Arrow in U.S. who in turn order from the factory. While that
distinction may sound minor, the US-based parent won't move until it has factory
MOQ orders in hand from its downstream. That means we can wait an indefinite
time for parts through "our" franchised distributor simply because of their
organisational structure. We had to wait 14 weeks for a Maxim eval kit that
was ex-stock Maxim throughout the entire waiting period because of this "food
chain". We also have to order factory MOQ as this sytem does not warehouse or
break down factory MOQ at any point.

As an alternative, there is a Maxim distributor next door (in N.Z.) who doesn't
seem to have the same hangups. His delivery is typically a couple of weeks vs
many months via the "official" chain - AND we get to order 20 chips instead of
500. So when we needed 20 chips for a pre-production run, guess which small
distributor got the business.

They also receive full technical support
from manufacturers (as opposed to having to ask questions on Usenet)

Not with Arrow Aust. If it isn't on the chip manufacturer's website then you
may as well forget it - or ask on usenet. Maybe they aren't representative of
authorised/franchised distributors elsewhere, but they certainly don't support
your model.

 

[Michael Kr?mer]

1. Is there any way to do a quick check on a microprocessor to

determine if it's "alive"? I realize manufacturers use million-dollar
testers for functional testing, but is there a way to "generically" do
a quick check on the bench using standard test equipment?

What you have in mind is a real challenge! A semiconductor
manufacturer is happy, if the test coverage exceeds 95% of all the
nodes inside the chip. That means that roundabout 5% of the chip
remains untested. And that is done with very sophisticated and
expensive test equipment, which can access the internal test logic. In
addition to the very fundamental IDDq test (measuring the qiescent
current), this results in a failure rate of a few ppm at the customer.

Without access to the test structures inside the device and without
thorough understanding of its design, you will hardly ever test more
than a third of the device with any test software. The other simple
tests which have been proposed here in other posts, will probably not
cover more than just 5 to 10% of the device.

One can find about 70% of all possible failures by means of dedicated
test software. We have done that for a 32-bit RISC CPU. It requires
the RTL description of the device and many days of simulation time per
iteration on expensive machines with even more expensive software.

The most simple test that you could do is the IDDq test (assuming the
device is CMOS and fully static). Measure the current consumption of
the device during Reset and then clock the device slowly. Measure the
static current after each clock edge. If it is more than the specified
leakage current, then discard the device. This test can find more than
50% of all possible bugs and therefore it is better than most test
software (which would still increase the coverage though). The idea
behind the IDDq test is that a failure will probably be caused by a
gate that is stuck at high or stuck at low, i.e. a transistor that is
constantly switched on or off. If the other transistor switches on,
then a short circuit exists and the leakage current is increased. Note
that such a short doesn't draw amps, but microamps...

2. Ditto for speed? How can one determine if a microprocessor will run
at its marked speed on a bench?

Run the device at nominal conditions (specified voltage and room
temperature) and use 1.5 times the specified clock frequency. That
should assure that the device works at minimum voltage and maximum
temperature at the specified speed.

I hope that helps.

Michael

 

[geneguy]

Not always the case. Here in down-under-land, Maxim (as one example, also
LinearTechnology) are officially distibuted by Arrow Electronics Australia,
AFAIK a wholly owned subsidiary of Arrow Electronics in the U.S. Arrow Aus
order through Arrow in U.S. who in turn order from the factory. While that
distinction may sound minor, the US-based parent won't move until it has factory
MOQ orders in hand from its downstream. That means we can wait an indefinite
time for parts through "our" franchised distributor simply because of their
organisational structure. We had to wait 14 weeks for a Maxim eval kit that
was ex-stock Maxim throughout the entire waiting period because of this "food
chain". We also have to order factory MOQ as this sytem does not warehouse or
break down factory MOQ at any point.

As an alternative, there is a Maxim distributor next door (in N.Z.) who doesn't
seem to have the same hangups. His delivery is typically a couple of weeks vs
many months via the "official" chain - AND we get to order 20 chips instead of
500. So when we needed 20 chips for a pre-production run, guess which small
distributor got the business.

I myself have used independent distributors to cover small-quantity
shortages as the original poster mentioned. Other OEMs do the same -
their buyers do this "under the table" so to speak (off the approved
vendor list). If the material is in original boxes then you can safely
say it's ok. All bets are off if the seal has been broken. I had one
batch with dead parts once. Failure analysis showed wrong die inside -
the outside marking was bogus.

Not with Arrow Aust. If it isn't on the chip manufacturer's website then you
may as well forget it - or ask on usenet. Maybe they aren't representative of
authorised/franchised distributors elsewhere, but they certainly don't support
your model.

By contractual agreement franchised distributors can refer their
customers to manufacturers for technical support (because the
questions tend to be application-specific and distributors are just
basically warehouses), and manufacturers are pretty supportive about
it in my experience. Independent distributors are not recognized by
manufacturers. As a matter of fact independent distributors are often
considered the cowboys of the industry, peddling parts of unknown
origin. Having said that, there is a place for them in the food chain.
You just have to be really careful.

 

[budgie]

I myself have used independent distributors to cover small-quantity
shortages as the original poster mentioned. Other OEMs do the same -
their buyers do this "under the table" so to speak (off the approved
vendor list). If the material is in original boxes then you can safely
say it's ok. All bets are off if the seal has been broken. I had one
batch with dead parts once. Failure analysis showed wrong die inside -
the outside marking was bogus.


By contractual agreement franchised distributors can refer their
customers to manufacturers for technical support (because the
questions tend to be application-specific and distributors are just
basically warehouses), and manufacturers are pretty supportive about
it in my experience. Independent distributors are not recognized by
manufacturers. As a matter of fact independent distributors are often
considered the cowboys of the industry, peddling parts of unknown
origin. Having said that, there is a place for them in the food chain.
You just have to be really careful.

Our experiences certainly differ. After waiting over three months for the "ex
stock" Maxim eval-kit, we commenced our product design in parallel with
evaluating the eval-kit. (Normally these would have been sequential but we had
lost 12 weeks).

A couple of complex design questions arose. I wasn't about to waste more time
dealing with/through the franchised distributor. I just fired emails into Maxim
tech support. They neither asked nor presumably cared where the parts were
sourced. I got exceptional one-to-one tech/design support.

We don't go down dark alleys seeking cheaper sources. We use known (and
long-standing) suppliers but don't get hung up on where they stand in the
official food chain. And we DON'T go anywhere near Arrow Aust any more.