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Topic: Alternative use of pins (Read 947 times) previous topic - next topic

afremont

#15
Mar 16, 2013, 06:55 am Last Edit: Mar 16, 2013, 06:59 am by afremont Reason: 1
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.
Experience, it's what you get when you were expecting something else.

ODwyerPW

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
Quiero una vida simple en Mexico...nada mas.

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