Power On States of Counters

Discussion in 'General Electronics Chat' started by DC_Kid, Mar 6, 2008.

  1. DC_Kid

    Thread Starter Distinguished Member

    Feb 25, 2008
    638
    9
    i'm deploying this 4bit counter (HEF4520B) in my automotive application. question is, when these counters power on what are the output states? will it power up with with outputs set to zero, or is there a possibility it could power on and have random outputs set high? this is important info for my application and as such i do not want to build in a timed master reset after power on before it can be used, etc.

    thanks
     
  2. nomurphy

    AAC Fanatic!

    Aug 8, 2005
    567
    12
    Your question is one that designers have pontificated over for decades now. But, long ago, lead to the invention of the Power On Reset circuit (also know as ~POR, *POR, POR*, !POR, /POR -- as it's usually active low).

    This circuit holds the remaining circuitry in reset (outputs set to a known state or are tri-stated) until such time that applied power is deemed good. This can be done with a simple RC network, but specialty IC's can also be used such as MAX708, or MAX 709, and many others of similar ilk (not limited to Maxim).
     
  3. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    There is a counter/timer IC that has a built-in selectable "power-on-reset". The CD4541.
     
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