I/O Multiplexing

Each pin is by default controlled by the PORT as a general purpose I/O and alternatively it can be assigned to one of the peripheral functions.

The following table describes the peripheral signals multiplexed to the PORT I/O pins.

Table 1. PORT Function Multiplexing
No PAD EXTINT PCINT ADC/AC OSC T/C # 0 T/C # 1 USART I2C SPI
1 PD[3] INT1 PCINT19 OC2B
2 PD[4] PCINT20 T0 XCK
3 PE[0]   ACO    
4 VCC
5 GND
6 PE[1]      
7 PB[6] PCINT6 XTAL1/TOSC1
8 PB[7] PCINT7 XTAL2/TOSC2
9 PD[5] PCINT21 OC0B T1
10 PD[6] PCINT22 AIN0 OC0A
11 PD[7] PCINT23 AIN1
12 PB[0] PCINT0 CLKO ICP1
13 PB[1] PCINT1 OC1A
14 PB[2] PCINT2 OC1B SS
15 PB[3] PCINT3 OC2A   MOSI
16 PB[4] PCINT4   MISO
17 PB[5] PCINT5   SCK
18 AVCC
19 PE[2]   ADC6    
20 AREF
21 GND
22 PE[3]   ADC7    
23 PC[0] PCINT8 ADC0  
24 PC[1] PCINT9 ADC1  
25 PC[2] PCINT10 ADC2
26 PC[3] PCINT11 ADC3
27 PC[4] PCINT12 ADC4 SDA
28 PC[5] PCINT13 ADC5 SCL
29 PC[6]/RESET PCINT14
30 PD[0] PCINT16   RXD
31 PD[1] PCINT17   TXD
32 PD[2] INT0 PCINT18