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Author Topic: Alternative use of pins  (Read 900 times)
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texas
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According to the Uno R3 schematic, there are no pullup resistors on pins 0 and 1.  It is normal for TTL serial signals to idle in a high state (+5V).  The 5mA current limit that Nick sees on one pin is because there are 1k series resistors in the TX and RX lines leading from the mega16u to the mega328p.  The other smaller current limit is probably the internal pullup on the RX line of the mega328.  While the mega16u would be continually trying to drive the pin high as Nick says, I believe that the mega328 pin could easily override the 5mA driving force when in output state.
« Last Edit: March 16, 2013, 12:59:48 am by afremont » Logged

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Thanks for this info. I have a project on an Arduino Pro Mini where I was 2 pins short (everyone appreciates an audible alarm and then a button to silence/acknowledge it!).
Now I will repurpose all 6 of the analog inputs as digital inputs and leave pins 1 & 2 available for serial communications in the future (Should I need it). That's puts me up 2 pins now!

Peter
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