shared i/o single pin
bozo
Posts: 70
Hi all
(a) To use a pin as either an input (connected to a switch/resistor cct) or an output (the pin is also connected to an LED/resistor cct)
should be quite simple. Whether the pin acts as an input or an output will vary at run time, so I want the cct
to be safe, ... any pointers?
(b) is it just me or is the search button at the top of this page really weak? Whenever I enter more than a few comma-delimited words I always get no results.?
cheers,
MArk
(a) To use a pin as either an input (connected to a switch/resistor cct) or an output (the pin is also connected to an LED/resistor cct)
should be quite simple. Whether the pin acts as an input or an output will vary at run time, so I want the cct
to be safe, ... any pointers?
(b) is it just me or is the search button at the top of this page really weak? Whenever I enter more than a few comma-delimited words I always get no results.?
cheers,
MArk
Comments
a) The main issue is whether the pin will be subjected to voltages greater than 3.3V or less than 0V. If so, the current has to be limited to < 500uA, usually using a series resistor of an appropriate value depending on the voltages involved. It is best to limit the current into or out of an I/O pin to 40mA or less. The Propeller's I/O pin structures seem to be capable of tolerating short circuits in output mode, but the official current limit is 40mA. There are also limits on total current in any group of 8 I/O pins and total current for the whole chip. Check the datasheet for details.
If you use the LED and series resistor to 3v3 and the switch to gnd this should work provided you cannot short the switch while the prop pin is an output. If this is possible then use a series resistor to the switch from the prop pin - a 1K should do.
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