a basic query

Discussion in 'General Electronics Chat' started by night crawler, Jul 28, 2008.

  1. night crawler

    Thread Starter New Member

    Feb 27, 2008
    well can smbody pls tell me what voltage values r associated with logic levels 0 & 1 . is it always
    0v for logic zero
    & 5v for logic 1 ?
  2. thingmaker3

    Retired Moderator

    May 16, 2005
    Designers have several choices. A positive voltage can represent logic zero & ground can represent logic one. This was once called "negative logic." Or the opposite may be used, as is more often the case. We used to call this "positive logic."

    Voltages can be five volts, three volts, twelve volts, or any other value needed for the specific application. Most commonly, we'll see devices running at either 5Vdc or 3.3Vdc, and using positive logic.
  3. SgtWookie


    Jul 17, 2007
    Sometimes it's defined by the family of logic devices. In the good old TTL series, a logic 0 was anything below 0.8v, and a logic 1 anything above 2.8v - even though powered by 5v (+/- 0.25v)

    4000-series CMOS can be used from around 3v to 16v. If Schmitt-trigger inputs are used, anything lower than 1/3 Vdd (Vdd = the positive supply voltage) is a logic zero, and anything higher than 2/3 Vdd is a logic 1.
  4. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    Here's a chart I ran across for 5V logic for various logic families.


    Best bet is to look at the data sheet for the specific digital logic or microcontroller chip your're using. Google is your friend there. ;)