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i want to know how to set unused pins of ic to gnd or vcc

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i want to know how to set unused pins of ic to gnd or vcc for safety

and i want to know also how to use some gates of the ic not all for example i want to use 3 gates of not ic and set the rest to vcc or ground

and i want to use 2 in an ic and the 3rd one in a new ic

  • Hi, If you have a multiple gate IC you can effectively ignore the gates you are not using. If you accidently ground an output that is trying to go high you will just increase the power consumption of your circuit. The gates in a multiple gate IC are separate and will not interfere with each other. Unless you are using the particular gate I would ignore, and let float its inputs and output pins.  It is a good idea to consult the data sheet on your IC for the manufacturers recommendation. Some specialty ICs can be programmed to do different things depending on grounding or pulling high designated pins.

    When I posted this I reply I thought we were discussing prototyping construction. If this is about Eagle then I will defer to someone else to answer the question.

  • Theoretically, depending on the chip's internal structure, unused digital inputs can switch randomly on local noise which can increase circuit noise or they can float into the linear region causing excess current to flow. This may not be an issue with your chips and I don't actually recall seeing this happen on an unused input, perhaps because I always connect them to a power rail. (I've been "told" it is good practice to always connect them for the above reasons.) You can connect these pins to power rails (from the supply library) with the WIRE tool or you can connect a short wire and name it GND or any other power rail name used in your circuit using the NAME tool.

  • in reply to dougw

    Hi Doug, Thanks for correcting my advice. I can see where pulling the inputs High would have no real effect on the power consumption while taking the possibility of noise from floating inputs out of the list of things that can go wrong. I am assuming that the unused outputs are left unconnected in whatever state they find themselves. Since I have had no formal electronics education and I do not remember anything in any of the texts that I have read that talk about unused pins I mistakenly assumed that floating inputs would be of no consequence.

    John