digital schematics are just topology

Discussion in 'General Electronics Chat' started by relicmarks, Nov 10, 2008.

  1. relicmarks

    Thread Starter Active Member

    Oct 13, 2006
    When you guys looks a schematic circuits for digital circuits/networks how do u do the circuit analysis for each inputs,outputs,etc for every pin on every IC chip?

    When i look at a schematic i always thought it was just a topology of trace routing and schematic symbols of electronic parts , thats all it was suppost to tell you was just the topology,trace rountings,symbols of electronic parts,grounds, supply voltages, how the parts and traces are hooked up which is topology

    A schematic doesn't tell you the waveforms , what they look like on every input and output , etc for each pin of every IC chips or component on the schematic or a stuffed PCB board circuit DUT device under test

    Schematics for digital electronic circuit is even worse can i need truth tables applied to the schematics , what would this be called? to have each input and output be Marked with either a 1 or O to tell me thats what it should be?

    Most of the schematics for digital electronic circuits are just left Blank with nothing telling me

    So how do i know if its a 1 or 0 or inverted by than? unless i sit there and do circuit analysis or reverse engineering analysis
  2. mik3

    Senior Member

    Feb 4, 2008
    Can you post an example of these schematics as we can see it and then discuss about it.
  3. relicmarks

    Thread Starter Active Member

    Oct 13, 2006
    any schematic, all the schematics i seen for RF,Analog and digital all don't have the waveforms or logic states on the schematics

    I need to know what frequency,waveforms shape,DC/AC voltages or logical state either its toggling or high or low are on each IC pin input,output,etc

    The schematics don't tell you any of these information at all, so how am i suppost to know this information if im not the designer ?

    Why is that schematics don't tell you this information? but what would if schematics don't?

    Most of the technical writes up i have at my jobs don't give any of this information either, mostly its just a Mr. Goodwrench telling to me replace IC chip after IC chip and after you do it the circuit still doesn't work

    The Technical writes up don't tell me what the waveforms or logical states are on the inputs or outputs of the IC chips , but this is the information i need mostly not the schematics

    How do i know if the inputs or outputs are::
    1.) Toggling from high to low
    2.) Toggling from low to high
    3.) HIGH
    4.) LOW
    5.) suppost to be Inverted
    6.) Toggling with DC offset ( i have found) toggling from +2volts to +7 volts
    7.) Is it positive logic or Negative logic at what theshold voltages

    Schematics don't tell you any of this information, for each IC input and output for every STAGE/section

    What would tell me this please?
  4. beenthere

    Retired Moderator

    Apr 20, 2004
    While in the world it is correct to recall that the map is not the territory, logic drawings are not subject to those problems. A well-designed system is over determined, meaning that every output may be predicted from any input. There are no areas of uncertainty.
  5. scubasteve_911

    Senior Member

    Dec 27, 2007
    I think what you are trying to learn is a dying art. Microcontrollers, FPGAs, DSPs are replacing a lot of these older designs which used a lot of digital logic. Without code or a good idea of what the circuit is trying to accomplish, diagnosis is very difficult.

    However, from a schematic point of view, one should be able infer much functionality. You should be able to test that each component is performing the intended task. The simplest example, an inverter, you are getting pulses / signals on the input, and the inverted signals on the output.

    Threshold levels are given in the datasheets and are related to the logic family being used.

    Unfortunately, schematics do not tell you everything you need to diagnose a circuit.