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Microprocessor question

Discussion in 'Electronic Basics' started by gary s, Oct 26, 2004.

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  1. gary s

    gary s Guest

    I have a question that I hope someone on here can answer, or give me
    an insight:

    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?

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

    3. If there is a "generic" feature set that is common to most
    microprocessors, and what might that be?

    4. How can one check for this - as far as hardware and software

    I guess I am looking for a "generic" test setup that can do something
    like a bare-bones electrical QC on different microprocessor families.

    Thanks for your help.

  2. Joerg

    Joerg Guest

    Hi Gary,
    Tough. The only crude way I have used in the past is a coil placed on
    top of it in a precisely repeatable position and looking at the
    spectrum. But that is crude and only comparative. I just needed it to
    see if something was running on it and to figure out if any of the
    spectrum would be synchronous to noise I was chasing.
    Only via a full electrical test, since all its functions must keep up at
    the rated speed.
    For me it is the noise spectrum emitted from the enclosure and the lines
    but that is different for every processor and circuit board. Kind of
    like submarine guys who are able to determine what kind of vessel is
    cruising above just from hearing its noise.
    It'll be different for every processor and you would have to obtain the
    QC procedure from the manufacturer, if they are willing to share it for
    incoming QC purposes.

    Regards, Joerg
  3. Rich Grise

    Rich Grise Guest

    Use a scope. The clock should be clocking, and the address, data, and
    control lines will all be going up and down, assuming it's executing

    Issue a reset, and you should see some kind of change in the waveforms.
    Build up the circuit, and test it. I think it's extremely unlikely that
    you'll get one that doesn't meet its own spec.

    If you're at the chip factory, and they're chips coming off the line,
    then shame on you! ;-)
    More or less - they have all the features of a processor. Clock,
    address, data, ALU, some control logic. Other than that, it's a
    free-for-all. ;-)
    In-circuit test is the only way to really verify the whole thing,
    and this shouldn't be in the end item, but a dedicated bench
    fixture with some diagnostic firmware and misc. peripherals and
    stuff, which will depend on your needs there.
    I'm afraid each family will need its own tester, or at least personality

    I don't even know if any manufacturers sell different versions that are
    plug-compatible, except maybe versions of the HC11 or so. But from
    one manufacturer to another, they're different enough that this would
    be a wild goose chase.

    Sorry I couldn't be more helpful.

    Good Luck!
  4. Of course. Plug it into a known-good mobo, fix a heatsink
    & boot.
    Leave booted for a while and watch for lockups.
    You could try running one of my cpuburn utils
    Yes, the x86 instructions set is common to all x86
    processors. At least the original IBM PC BIOS tested
    some basic functionality.
    There are pgms that will check operations.
    JTAG might work if you've got the money.

    -- Robert
  5. If you're testing older processors such as the Z-80 and the 6502, you could
    buy some cheap PCs such as the TRS-80 (Z-80), an Apple II (6502), a Radio
    Shack Color Computer (6809) and/or an original Macintosh (68000) and use the
    sockets on the motherboards or install one if not already provided. Then
    just use each computer as a test bench.
  6. gary s

    gary s Guest

    Thanks for all the prompt replies I've seen so far.

    I work for a reseller, and my company acts as the broker for large
    batches of different types of microprocessors bought on the "gray"
    market to meet production shortages. There is no longer any
    manufacturer's warranty, therefore there is a desire to screen out
    parts that are dead, slow, or counterfeit. It appears there are folks
    out there who are making a living remarking slow parts, or assembling
    parts that have been scrapped off the manufacturer's production

    I've been told that after a microprocessor leaves the manufacturer,
    there is really no way to test it except on a motherboard/application
    board (or some kind of evaluation board). My customers are doing this
    after their assembly process. But it would be nice to have some kind
    of meaningful acceptance testing at my end before they get the part.

    I've received suggestions that (1) maybe there is a way to see if the
    thing wiggles (the assumption is if you can wiggle it (maybe getting
    it in and out of reset?), it's probably good - or there is a live chip
    inside anyway), and (2) maybe there is a way to do something like
    adding 2 and 2 (or loop on something) to see if the thing can perform
    at the advertised speed.

    Evidently I would need the services of an EE to attempt something like
    this. And if this "generic microprocessor checker" can be built, I
    suspect it's going to be a challenge mechanically, owing to all the
    different pin-outs and package types. I just wanted to know from the
    experts on here if this is something that is worth pursuing, or
    proposing to my management.

    Thanks again -

  7. budgie

    budgie Guest


    Because of the diversity of types/pinouts I suspect you are chasing the
    unachievable unless you have a '70s NASA budget.

    What you COULD do is consider moving the client testing into YOUR facility. If
    they can provide either end-product or a test jig for the specific micro they
    purchase, your outfit could do the testing before on-shipping the chip. That
    would relieve them of that burden and give your firm not only confidence in the
    shipped part but also a reputation for actually giving a stuff about the client.
  8. Rich Grise

    Rich Grise Guest

    Hear! Hear! This is actually a very good idea.
    Guess I'm getting old in my old age. ;-)

    Have Fun!
  9. Tom Seim

    Tom Seim Guest

    Do you have a known "good" board?

    If so, you can probe around with an oscope and you will get some
    repeatible waveforms. Now go to your "bad" board and do an A-B
    comparison. With some trial and error you will find some waveforms
    (pins) that will give you a "state-of-health". And this without
    knowing anything about the processor or application.
  10. Bill Bowden

    Bill Bowden Guest

    Just use a scope and look for square waves on various pins of the
    micro. That will tell you something is happening, maybe correct,
    maybe not. If you don't have a scope, use a DMM to measure the
    DC voltage on various pins. The DC voltage will vary from 0 to 5 volts
    or 0 to the power supply voltage indicating something is happening on
    that particular pin. But it's hard to tell exactly what is going on
    without knowing the program. And then it would be difficult to
    interpret the digital signals from the program. If you have a good
    micro, you can compare the waveforms of the test micros to the known
    good micro and usually identify the problems.
    You probably need to use a external clock to drive the micro
    at the rated speed or greater.
    A generic feature would be the number of I/O lines and internal
    program RAM and ROM available.
    Is this a homework problem?
    You need different tests for different processors. The pin assignments
    will be different, so you have to look at different pins for different
    activity of different processors.

  11. It is not beyond feasible to build a test jig for each microprocessor

    For example, I've been messing about learning the 8051 processor family. I
    have an EPROM / Flash programmer I bought new from ebay for about $45 which
    will program almost everything. My "Test Jig" consists of a prototyping
    breadboard into which I've plugged a simple power supply, the processor
    (with onboard flash memory), one crystal and 2 capacitors (for the clock)
    and a reset switch. You can write a trivial looping program to output a
    square wave, program the processor using your PC, use the maximum crystal
    frequency, and see if you get a square wave. For processors without onboard
    program space you can add an EPROM to the breadboard and blow that instead.
    This jig should work for all processors in the 8051 family of the same
    package (number of pins). This will indicate the processor can run a basic
    function at maximum rated speed. There could be other faults of course
    (falty onboard RAM) but it sounds like this simple test is what you need.

    If all this sounds too daunting, get a Microprocessor Programming book and
    spend a few evenings reading it, and you may find it's well within your own
    capability. This isn't rocket science despite appearances.

  12. You're right about a microcontroller like the 8051. But the common
    microprocessor has more than ten times the number of pins, and it's a
    lot more than rocket science to get it running without any support
  13. Tam/WB2TT

    Tam/WB2TT Guest

    What I have done to test a new board is to write a simple program that
    executes on power up:
    1) write 55 to some memory location
    2) write AA to same memory location
    3) Read memory location
    4 loop back to 1)

    Hor an Intel type chip, I also did an IOR and IOW.

    This obviously requires different hardware for each type of chip. I don't
    see any way around that.

  14. CWatters

    CWatters Guest

    Most single chip micros will configure all the pins as inputs on Reset/POR.
    Early in the code the programmer has to configure the pins to be inputs or
    outputs. If you see all the pins floating or pulled hi/low by external
    components then it probably hasn't executed that early code. If we are
    talking about a new flash programmable part then it's also possible someone
    forgot to program it (eg it's still blank!).
  15. CWatters

    CWatters Guest

    Please let us know who your customers are so we can avoid buying from them!
  16. Wim Ton

    Wim Ton Guest

    Elektor magazine had a suggestion way back: fill a memory with NOP's
    suitable for the processor. If everything is working, you should see halving
    the frequency on every higher address line. And you may use a variable clock
    source to see when things start to go wrong.

  17. Rich Grise

    Rich Grise Guest

    I believe you've just invented the "signature analyzer." :)

  18. gary s

    gary s Guest

    Chances are you have something in your house from one of my customers.
    But rest assured their outgoing QC is 100%.

    A lot of my inventory comes from OEMs in sealed, virgin condition so
    there is little that needs to be done. There is a huge market for
    excess and obsolete parts, and there is always a demand somewhere for
    them. Unfortunately, it is the stuff of questionable pedigree that's
    giving everybody headaches.

    Regards -

  19. gary s

    gary s Guest

    This is similar to what was suggested to me. My problem is in somehow
    "generalizing" this to a superset to include 16 and 32-bit parts with
    hundreds of pins.

    Thanks -

  20. Yes, sorry about that, I was assuming the poster was talking
    microcontrollers in consumer equipment rather than big computing systems. I
    see a lot of this stuff.
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