logic scopes and logic analyzers

Discussion in 'General Electronics Chat' started by relicmarks, Mar 30, 2008.

  1. relicmarks

    Thread Starter Active Member

    Oct 13, 2006
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    What kinds of test and measurements can logic analysers do please?

    what kinds of test have you guys done in jobs or personal use when logic analyers?
     
  2. relicmarks

    Thread Starter Active Member

    Oct 13, 2006
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    types of logic measurements would be?

    1.) Jitter- time differences from input square waveform compared to output waveform?

    2.) To see if the Clocks were all in sync?

    3.) Check the "timings" of the what?
     
  3. beenthere

    Retired Moderator

    Apr 20, 2004
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    I used one at work many years ago. I can't imagine using one as a piece of home test equipment.

    I was using it in the logic plane of a microfilm printer, although they can be used on data buses, too. The one I used allowed you to have 9 traces on your oscilloscope CRT that would indicate the state of the logic element each probe was attached to.

    Triggering could be off the 9th trace, or a combination of several other inputs. The display could run from either the moment of trigger, or from several clock periods before the trigger went true.

    Jitter was never a problem in my application - timing was in the low MHz range, to timing differences across a motherboard did not happen.

    There should never be multiple clocks in a system. There may be timing signals running at different rates, but they need to be derived from the master clock. Otherwise, all is chaos.

    Everything in a system is clocked. It can be as simple as Read/Write, or be more complex. But certain functions have to happen at predictable times. Logic analyzers are very good at establishing timing relationships for a number of signals.

    I would hate to have to mess with more than 9 traces. Even with color, trying to make sense of 16 or 32 traces would be mind-boggling.
     
  4. relicmarks

    Thread Starter Active Member

    Oct 13, 2006
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    1.) triggering problems like what on the logic analysers or O-scope?
    2.) sync problems like what on the logic analyser or O-scope?
    3.) Timing difference problems like what on the logic analyser or O-scope?


    How would i know if i had triggering problems? sync problems? or timing problems in my digital circuits please?

    What other digital waveform problems would i be looking for as a digital test tech or troubleshooting digital circuits please?
     
  5. beenthere

    Retired Moderator

    Apr 20, 2004
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    My experience suggests that most industry jobs tend to involve only limited subsets of the electronics field. If you have the basics down, you can build on that to produce the skill set your employer needs. I learned electronics when nearly all transistors were PNP germanium, and all computers were discreet DTL logic. I ended up spending 24 years at a major university designing, building and repairing anything that came in the door (and much of which had no documentation).

    There is a corollary to the above - you can't learn everything about something before you need to use that knowledge. book learning is not the same as experience.
     
  6. relicmarks

    Thread Starter Active Member

    Oct 13, 2006
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    can you please give more info then about the questions to help out
     
  7. lightingman

    Senior Member

    Apr 19, 2007
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    Hi,

    I use logic analysers all the time at home in the workshop....
    If you are working with PIC's and and addressing other devices in both parallel and serial formats. they are a valuable tool for looking at the timing of the signals and for glitch detection...

    I use have 3 x Tektronix 1240's, 2 x Sony/Tektronix 308's, 1 x HP1631D, 1 x HP1600, 2 x Thandar LA160's and 1 x Gould K100.

    Daniel.
     
  8. techroomt

    Senior Member

    May 19, 2004
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    i can't imagine any one piece of test equipment more useful in analyzing digital data. the models (HP) i used had multiple pods with each pod having 10 hookup capability. it takes some time to set-up the device with connections and bit groups, as well as trigger. the device has memory, similar to a fifo, with selectable timebase, where the trigger can be placed somewhere in the allowable time window, so that you can look at the events prior to or after the valid trigger. a valid trigger could be a write enable, or board address, or any bit combination you desire.

    you can look to see if the appropriate data was available at the inputs when the control signals arrive. or did the control signals arrive at the correct time. did the outputs corrspond correctly. was the bus tri-stated/is there bus contention. it gives you the opportuniy to evaluate groups of digital data at it's level, at it's speed. whereas an oscope, can only asses data with the number of channels it has (usually 2).
     
  9. relicmarks

    Thread Starter Active Member

    Oct 13, 2006
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    What types of digital signals would i be looking at?

    1.) control signals?
    2.) Data signals?
    3.) trigger signals?
    4.) write enable signals?
    5.) board address signals?
    6.) bit combination signals?
    7.) parallel and serial address signals?
    8.) timing of the signals?
    9.) glitch detection signals?
     
  10. techroomt

    Senior Member

    May 19, 2004
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    yes to 1-9. although glitch detection would be something you analyze form the received data.
     
  11. relicmarks

    Thread Starter Active Member

    Oct 13, 2006
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    Can you list any more?
     
  12. relicmarks

    Thread Starter Active Member

    Oct 13, 2006
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    What are some TTL timing problems?

    What are some CMOS timing problems?

    What ares some DTL timing problems?
     
  13. techroomt

    Senior Member

    May 19, 2004
    198
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    timing problems (for all) can be evaluated: basically the signals can be looked at as far as their arrival and departure from a point/input respective of the other signals. e.g. does a control signal (write enable) arrive after all of the data inputs have settled, or did the address bus enable a board prior to the data words being present. it can be used on a backplane (control/address/data) bus, or used to look at signals on a chip level. this often requires looking at the data sheets for the components you're evaluating for the timing criteria and constraints of the device.
     
  14. relicmarks

    Thread Starter Active Member

    Oct 13, 2006
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    How do you know if the digital logic state is OPEN? not high or low but OPEN? how would i measure that ?
     
  15. techroomt

    Senior Member

    May 19, 2004
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    the analyzers i used (hp) displayed a "0" for a low, a "1" for a high, and an "x" for indeterminate state - outside the ranges of a logic 1 or 0. otherwise i am not sure what you mean by a logic "open". are you referring to an open circuit (no contimuity)? if so the analyzer would likely show an x or maybe float high.
     
  16. relicmarks

    Thread Starter Active Member

    Oct 13, 2006
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    on my logic probe i have a high,low, open LED

    but i don't know when there is a "logic open"
     
  17. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    For example when you use tri-state buffers, which can be high, low, or not connected at all. They are used on busses, where many devices have connected outputs.
     
  18. relicmarks

    Thread Starter Active Member

    Oct 13, 2006
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    So tri-state buffers are digital?

    How would i know if im reading a FLOATING digital signal? how would i tell that its floating ? (not high or not low ) its floating between high and low



    Digital troubleshooting:

    1.) There is No digital input to the chip
    2.) There is No digital output to the chip
    3.) Check the Vcc voltages and grounds to the chip
    4.) Either the chips output is stuck in a high state or low state or its dead or open
    5.) The pull up resistor is open or shorted
    6.) What else can be wrong when troubleshooting digital circuits?
     
  19. relicmarks

    Thread Starter Active Member

    Oct 13, 2006
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    Digital troubleshooting basics list

    Digital troubleshooting basics list :

    1.) There is No digital signal to the input of the chip
    2.) There is No digital signal of the output of the chip
    3.) Check the Vcc voltages and grounds to the chip
    4.) The output of the chip is not pulsating high or low but is "stuck" in a high state or low state or its a dead line
    5.) The pull up resistor is open or shorted
    6.) The chips output voltage state is reversed polarity when it shouldn't be, its been inverted
    7.) Either the chips input or outputs are "floating" (not grounded) or open


    What else can be wrong when troubleshooting digital circuits?
     
  20. relicmarks

    Thread Starter Active Member

    Oct 13, 2006
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    1.) control signal problems or errors
    2.) Data signal problems or errors
    3.) trigger signal problems or errors
    4.) write enable signal problems or errors
    5.) board address signal problems or errors
    6.) bit combination signal problems or errors
    7.) parallel and serial address signal problems or errors
    8.) CMOS and TTL timing problems?
    9.) glitch detection signals
    10.) Syncing problems , is the sync is offset
    11.) Clock signal problems, clock phase, clock on/off duration time is wrong
    12.) Looking for Jitter- time differences
    13.) Looking for propagation delay on the inputs and outputs
    14.) Reset signals
    15.) latching signals
    16.) Timer signals


    ANY more guys that you can add to the list please?
     
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