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What is level triggering in digital ccts

  1. Sep 21, 2009 #1
    what is level triggering in digital ccts.

    I think borth level triggering and edge triggering are same.

    Because in a pulse streem, edge have a level. please help me.

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  2. jcsd
  3. Sep 21, 2009 #2
    Re: triggering

    hello asprilanka-
    There are two basic types of flip flops. One is edge triggered or D-type flip flop (74LS74). These depend on a minimum dV/dt to trigger efficiently. The other type is the level rtiggered, or JK flip flop (74LS73). These can trigger successfully on pulses with very slow rise and fall times, like sine waves.
    [Edit] The first TTL monostable one-shot to come out was the 74121. It was a difficult chip to work with because it could not be retriggered until it reset to the stable state. The 74123, which could be retriggered at any time, then came out.
    Bob S.
    Last edited: Sep 21, 2009
  4. Sep 21, 2009 #3


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    Staff: Mentor

    Re: triggering

    One difference is with edge triggering, you can chose + or - edge to trigger on. With level triggering, you just choose the voltage level to trigger on.
  5. Sep 23, 2009 #4
    Re: triggering

    Why not theare are 2 edge trigger types
    +ev edge triggering
    -ev edge triggering
  6. Sep 23, 2009 #5


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    Science Advisor

    Re: triggering

    There are devices that use rising edge triggering and devices that use falling edge triggering.
    This is always stated or shown in the data sheets.

    Here is a quote from the data sheet for the CD4020 and CD4040 binary counters:

    The CD4020BC, CD4060BC are 14-stage ripple carry
    binary counters, and the CD4040BC is a 12-stage ripple
    carry binary counter. The counters are advanced one count
    on the negative transition of each clock pulse. The
    counters are reset to the zero state by a logical “1” at the
    reset input independent of clock.

    Notice that the triggering is on the falling edge of the clock pulse but RESET occurs whenever the reset pin is taken high, so it would occur on the rising edge of this pulse.
    But, the reset does not have to have an actual pulse to work. You could turn the device on with the reset tied high and it would stay in reset mode until you removed the high.

    There are a few devices that let you choose whether the triggering is on the rising or falling edge of the clock square wave. One such device is the 74C221, a very versatile Monostable chip.
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