Greetings,
Jesse, you are a fountain of knowledge :) Thanks curtis too !
Sorry to insist again, ascii Schematics ;)
3.3V (Supply, DIO header)
|
R1
|
-
V (LED)
-
|
CPU Pin (DIO_08 = port F bit 0 ; LVTTL [logic 1 = 3.3V] )
So,
(3.3 - 1.6) / 0.0094
With red led, R1 = 180 (sink 9.4ma)
(3.3 - 1.6) / 0.0077
With red led, R1 = 220 (sink 7.7ma)
Is that safe to do that ?
What's exactly happen when DIO_08 is at logic 1 ?
Matthieu
Jesse Off wrote:
>Actually, you likely can connect an LED directly to a DIO port. You
>must be sure to *sink* current. Current ratings on CMOS output pins
>are determined based on max current that still result in a valid logic
>level. In the case of an 8mA rated output sinking its rated 8mA of
>current the voltage measured at the output pin is guaranteed to be <=
>0.4V (which is still a valid 0). If you exceed the current rating the
>voltage at the pin will rise to a point where it will no longer be
>interpreted as a valid '0' to another CMOS input (you can think of the
>output driver as a resistor to ground). Since you're driving an LED,
>not another CMOS input, it doesn't matter if the voltage rises a bit
>so you can squeeze a bit more than the rated current out of the pin.
>You wouldn't want to go a lot more than the rated current, but
>certainly another 2mA (total 10mA) is doable and perfectly safe.
>
>//Jesse Off
>
>
>
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