2 leds without resistor

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hi,

i'm new arduino. connected 2 leds in row output pin on arduino uno r3. it's working fine. read led has internal resistance of 100 ohm. 2 leds in row should split there 5 v 2.5v each. way should no problem leds, shouldn't it?

thanks help

worry microcontroller. absolute maximum current pins on uno 40 ma note datasheet says:
quote
exposure
to absolute maximum rating conditions extended periods may affect device reliability.
really shouldn't go on 20 ma. don't ruin uno skimp on $0.02 resistor!


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