Logic Gate Vcc and GND purpose?

Discussion in 'Digital Circuit Design' started by Nathaniel Zhu, Mar 25, 2016.

  1. Nathaniel Zhu

    Thread Starter New Member

    Oct 16, 2015
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    3
    Hey! So I'm looking at the pinout charts and simulating some circuits on 123dcircuits using the 74HC32 and so on.
    They all have VCC and GND pins but I can get the logic gate to work without them.

    Like for example, 74HC32 is 4 OR gates I think. 1A,1B,1Y which corresponds to the pins on the logic gate but VCC and GND doesn't fit anywhere?

    In fact, I don't see what purpose they have since vcc and gnd aren't part of the logic gate.
     
  2. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    1,512
    You may get them to work in what ever simulator your using, but not in a real circuit. Vcc and Ground are how the real chips are/will be powered. Without them the chip will not work.
     
  3. dl324

    Distinguished Member

    Mar 30, 2015
    3,211
    619
    If the simulator has explicit power connections for IC's, it shouldn't allow gates to function without them. If they're implicit, it's assuming the user knows enough to connect them.

    In the physical world, powering CMOS through inputs and/or outputs can damage them; either immediately or at some unknown future time.
     
  4. WBahn

    Moderator

    Mar 31, 2012
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    Many simulators, including some high-end simulators in years past, only concerned themselves with matching a device's behavior at the I/O pins. But that doesn't excuse sloppiness on your part. If you CAN connect power and ground, you should. You should also not leave unused inputs unconnected (unless that particular pin on that particular part is designed to be left unconnected).

    This may or may not affect the behavior of your simulation, but you will thank yourself once you start building circuits that have to work in the real world.
     
  5. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    If you use a CAD program to draw your schematic, such as Eagle, you may not find VCC or GND pins shown either. If that happens, you need an extra few keystrokes to show them.

    John
     
  6. ScottWang

    Moderator

    Aug 23, 2012
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    If you don't have the experience for logic gates, I suggest you to do the real practice, maybe using breadboard to connect the circuit, and using the multi-meter to measure the current for IC and its gates, also measure the voltages for the input and output for the gates, when you have more experience then you can using the logic gates simulation software, only doing the real experiments can build your logic foundation and ability to solve the problem when the problem happens.
     
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