schematics LED connection

[Altera_Forum]

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

And Fpga is directly connected with led then pull down?   Regards, shahul

[Altera_Forum]

use resister can reduce the current and the brightness of the led.

[Altera_Forum]

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

can any one differentiate it?  Regards, shahul

[Altera_Forum]

please reply to the above question?

[Altera_Forum]

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]

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]

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]

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