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    IC question (unused pins)

    Hi,

    I am using a 74LS157 (Quad 2 to 1 multiplexer). However I only need to use one of 2 to 1 multiplexer. My question is, should I ground the pins I don't use or leave them alone.

    Thanks

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    IC question (unused pins)

    in its datasheet it is given that:
    Note 2: Not more than one output should be shorted at a time.

    so you cant tie all output pins to either GND or VCC, so it is better to keep them open.
    About input i feel that it is better to keep them open

    regards
    JSPS



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    Re: IC question (unused pins)

    nwo4life,
    It's best to tie inputs to a state that will force the output to a known state. This way, the outputs can not bang up and down in response to noise on the open inputs, creating noise and emi.
    .
    For example, tie at least one input of an And or Nand gate to ground ("0"). Tie at least one input of an Or or Nor to "1". Tie clock inputs to eithe"0" or "1". If a device has a reset or clear input, tie one of them to the active state.
    .
    Regards,
    Kral



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    IC question (unused pins)

    the device you are using is a bipolar logic family (low power schottky). i usually just leave them floating because those devices are not prone to latch up due to external noise, unlike cmos logic devices. but Kral has a point, it is better if you force them to a known state. also see which output state gives you lower power dissipation, that's even better. the lower value of input current will give you the lower power dissipation. i think for ttl it is better if you force the output to logic hi. i'm nnot sure though... that depends on the output driver of your logic device.....



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    Re: IC question (unused pins)

    yippo! gelidude is right, just leave 'em floating and as is...



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    Re: IC question (unused pins)

    nwo4life,
    In re-reading my previous reply, I noticed a mistake, you should tie the unused reset or clear inputs to the "inactive" state. This probably does not apply to your multiplexer application, but it's imprtant when using flip-flops, counters, etc that have direct set or clear inputs.



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    IC question (unused pins)

    IT is better to leave them open.



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    IC question (unused pins)

    better leave them open
    regars



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