Port A
[Peripherals]

Port A structure

The port A offers 8 bidirectional general purpose IO lines.
Lines 0 and 1 also have alternate functions:

• line 0 can be used as external interrupt 0 input
• line 1 can be used as timer 0 clock input.

Port A is managed through 3 IO File locations: PORTA, DDRA and PINA.
DDRA sets each pin's direction: DDRA(i)=0 means that line i is input, DDRA(i)=1 means that line i is output.
When writing a value to the port, that value goes into PORTA. If DDRA configures the corresponding lines as outputs, the contents of PORTA will be available on external pins. However, if DDRA configures the lines as inputs (DDRA(i)=0), then:

• if PORTA(i)=0, the line i is `pure' input (High Z).
  
• if PORTA(i)=1, the line i is an input weakly pulled high.
  

PINA reads the physical value of external lines, rather than PORTA.

Port A schematics

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