Limitations on IO0 and IO1 ??

Hi,
I am trying to connect a led directly on IO0 and on IO1 (with a 220 ohm resistor in series with each LED). when I do that, communication with arduino stops.
I noticed that the IO0 and IO1 pins also have the TX and RX functionality.

is there any limitations on these pins that prevent me from connecting the leds as I wanted?

thanks!

What is the voltage on the pins when you output a high?
What is the USB/Serial chip? 16U2, FT232R, something else?

Try higher value resistors, like 1K, so less current goes into the LEDs.

my question was related to UNO, sorry for not mentioning in the original post. as such, I am using the USB connection provided by UNO.

increasing the resistor would definitely decrease the current, but also the light coming out of the LED, and that is not desirable.

Real Uno? or clone with CH430?

VOL Output Voltage LOW (draw 4mA current): 0.5 V
VOH Output Voltage HIGH (output 3mA current): Vcc = 0.5V

VOL & VOH with 12,13mA load? Who knows. What voltages are you seeing?

FT232R & 16U2 both have 20mA outputs.

Try high brightness LEDs instead, with lower current.

ZvikaRozenshein:
Hi,
I am trying to connect a led directly on IO0 and on IO1 (with a 220 ohm resistor in series with each LED). when I do that, communication with Arduino stops.
I noticed that the IO0 and IO1 pins also have the TX and RX functionality.

Exactly!

Ergo, you cannot use them as I/O if you want to have communication with the serial port.

How much simpler can it be?