View difference between Paste ID: Rr0cLEsg and YxbLF7Gi

 pin "high" = voltage close to i/o supply ("vdd" or "vcc")
 pin "low" = voltage close to ground ("vss" or "gnd")
 (The exact meaning of "close to" will vary.)
 
 
 driven high (output enabled, output high, internal pull-up/down irrelevant):
 - tries very hard to make voltage on pin high
 - current flows to the pin (from vdd) as necessary until the pin is high (or something breaks)
 - for BBB:  voltage will be at least 2.85V on condition that current does not exceed 4 mA
 
 driven low (output enabled, output low, internal pull-up/down irrelevant):
 - tries very hard to make voltage on pin low
 - current flows from the pin (to vss) as necessary until the pin is low (or something breaks)
 - for BBB:  voltage will be at most 0.45V on condition that current does not exceed 4 mA
 
 pulled up (output disabled, internal pull-up enabled):
 - weakly tries to make voltage on pin high
 - a small amount of current flows to the pin (from vdd) until the pin is high
 - for BBB:  max current is 0.243 mA
 
 pulled down (output disabled, internal pull-down enabled):
 - weakly tries to make voltage on pin low
 - a small amount current flows to the pin (to vss) until the pin is low
 - for BBB:  max current is 0.11 mA
 
 floating (output disabled, internal pull-up/down disabled):
 - also known as "high-impedance" or "high-Z"
 - tries to avoid having any influence on the voltage on the pin
 - very little current flows to/from the pin
 - for BBB:  max current is 0.018 mA
 
 
 input characteristics for BBB:
 - pin will be regarded as low when input is disabled or pin voltage is at most 0.8V
 - pin will be regarded as high when input is enabled and pin voltage is at least 2V