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Pins 7-10, Port C Bits 5-2
These pins may be used as general inputs or outputs.
Pin 11, Port C Bit 1 and Port D bit 3
In addition to being a general input or output pin, a signal may be applied to this pin to serve as external
Interrupt 1.  Port C Bit 1 must be an input for this to work properly.  Alternately, if no external signal is
connected, Port C Bit 1 may be an output and serve as the source for the interrupt.  Additionally, this pin
serves as the SDA line when using I2C channel 0.
Pin 12, Port C Bit 0 and Port D bit 6
In addition to being a general input or output pin, a signal may be applied to this pin to serve as the input
for the InputCapture() routine.  Port C Bit 0 must be an input for this to work properly.  Additionally, this
pin serves as the SCL line when using I2C channel 0.
Pins 13-17, Port A Bits 7-3
In addition to being general digital input or output pins, these pins may be used for analog input to the
analog-to-digital converter.  The analog voltage may be read using the GetADC() routine.
Pin 18, Port A Bit 2 and Port B Bit 2
In addition to being a general digital input or output pin this pin may be used for analog input to the
analog-to-digital converter.  Alternately, a signal may be applied to this pin to serve as external Interrupt
2.  Port A Bit 2 must be an input for this to work properly.  Moreover, if no external signal is connected,
Port A Bit 2 may be an output and serve as the source for the interrupt.  A second alternate use for this
pin is as the analog comparator input.  See the Atmel documentation for the AIN0 input for more details.
  
Pins 19-20, Port A Bits 1-0
In addition to being general digital input or output pins, these pins may be used for analog input to the
analog-to-digital converter.  The analog voltage may be read using the GetADC() routine.
Pin 21, Regulated Voltage In or Regulated Voltage Out
If the on-board regulator is being used (power being fed to pin 24) this pin will output a regulated voltage
of about +5 volts.  The capacity of the on-board regulator is approximately 100mA.  About 60mA of this
capacity is used by the on-board devices with all pins in the input state.  If any of the pins are outputs, the
source current of each output pin must be added to this usage.  The balance of the regulator’s capacity
(very little, in most cases) may be used by external circuitry.
Except for the simplest configurations, it is advisable not to use the on-board regulator and, instead,
supply a regulated voltage of 4.5 to 5.5 volts to pin 21.  In this case, no connection should be made to pin
24.
Pin 22, Reset
You may apply an active low signal to this pin to reset the processor.  Note, however, that the on-board
reset circuitry will also pull this line low via an open collector output each time the ATN input makes a
positive transition (notably during downloading).  If you don’t want your external circuitry to receive this
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