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	PTC X	PTC Y	OSC	T/C		USART	I2C	SPI
1	PD[3]	INT1	PCINT19		X3	Y11		OC2B
2	PD[4]		PCINT20		X4	Y12		T0		XCK0
3	PE[0]		PCINT24	ACO	X8	Y16		ICP4			SDA1
4	VCC
5	GND
6	PE[1]		PCINT25		X9	Y17		T4			SCL1
7	PB[6]		PCINT6				XTAL1/TOSC1
8	PB[7]		PCINT7				XTAL2/TOSC2
9	PD[5]		PCINT21		X5	Y13		OC0B / T1
10	PD[6]		PCINT22	AIN0	X6	Y14		OC0A
11	PD[7]		PCINT23	AIN1	X7	Y15
12	PB[0]		PCINT0		X10	Y18	CLKO	ICP1
13	PB[1]		PCINT1		X11	Y19		OC1A
14	PB[2]		PCINT2		X12	Y20		OC1B				SS0
15	PB[3]		PCINT3		X13	Y21		OC2A		TXD1		MOSI0
16	PB[4]		PCINT4		X14	Y22				RXD1		MISO0
17	PB[5]		PCINT5		X15	Y23				XCK1		SCK0
18	AVCC
19	PE[2]		PCINT26	ADC6		Y6		ICP3				SS1
20	AREF
21	GND
22	PE[3]		PCINT27	ADC7		Y7		T3				MOSI1
23	PC[0]		PCINT8	ADC0		Y0						MISO1
24	PC[1]		PCINT9	ADC1		Y1						SCK1
25	PC[2]		PCINT10	ADC2		Y2
26	PC[3]		PCINT11	ADC3		Y3
27	PC[4]		PCINT12	ADC4		Y4					SDA0
28	PC[5]		PCINT13	ADC5		Y5					SCL0
29	PC[6]/RESET		PCINT14
30	PD[0]		PCINT16		X0	Y8		OC3A		RXD0
31	PD[1]		PCINT17		X1	Y9		OC4A		TXD0
32	PD[2]	INT0	PCINT18		X2	Y10		OC3B / OC4B