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Altera_Forum's avatar
Altera_Forum
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15 years ago

schematics LED connection

what is difference when we connect resister b/w fpga and led,

And Fpga is directly connected with led then pull down?

Regards,

shahul

7 Replies

  • Altera_Forum's avatar
    Altera_Forum
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    15 years ago

    i have attached the two different type of interface with led.

    can any one differentiate it?

    Regards,

    shahul
  • Altera_Forum's avatar
    Altera_Forum
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    15 years ago

    I don't understand your question... putting the resistors before or after the leds doesn't change anything, as in both cases they are in series with the leds.

    But with 10k I don't think that you'll see a lot. Just check the LED datasheet for the recommended current and standard forward voltage, and determine the nominal value for your resistors.
  • Altera_Forum's avatar
    Altera_Forum
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    15 years ago

    Hi Daixiwen,

    why i ask this question is in our FPGA we have 8 leds connected as the top schematics shown in that figure.At the time of power ON all led glow. I don't no why this leds are glowing.it should be in off state.

    Regards,

    shahul
  • Altera_Forum's avatar
    Altera_Forum
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    15 years ago

    Before configuration all the pins have a weak pull-up, so this can explain why you see them glowing. It should be a lot dimmer than with an output pin at logical '1' though.

  • Altera_Forum's avatar
    Altera_Forum
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    15 years ago

    Mostly, people are operating LEDs with active low FPGA outputs and anode connected to 3.3V for the said reason.