6 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 6-1. PORT Function Multiplexing
14-pin	8-pin	Pin name	Special	INT⁽³⁾	ADC⁽³⁾	AC	USART	Timer	Programming⁽⁸⁾
1	1⁽¹⁾	V_CC
2	2	PA[0]⁽²⁾	CLKI	PCINT0	ADC0	AIN0		T0	TPICLK
3	3	PA[1]⁽⁵⁾		PCINT1	ADC1	AIN1		OC0B	TPIDATA
4	4	PA[2]	RESET	PCINT2					RESET
5	-	PA[3]⁽⁹⁾		PCINT3				OC0A
6	-	PA[4]⁽⁹⁾		PCINT4				ICP0
7	-	PA[5]⁽⁵⁾⁽⁹⁾		PCINT5	ADC2			OC0B
8	-	PA[6]		PCINT6	ADC3
9	-	PA[7]		PCINT7
10	-	PB[0]		PCINT8	ADC4
11	5	PB[1]⁽⁶⁾	CLKO	PCINT9/INT0	ADC5		XCK0	OC0A
12	6	PB[2]⁽⁷⁾		PCINT10	ADC6		TxD0	ICP0
13	7	PB[3]⁽⁴⁾⁽⁹⁾		PCINT11	ADC7	ACO	RxD0	T0
14	8	GND

Note:

On the 8-pin UDFN package, the thermal pad should not be connected as well.
Priority of CLKI is higher than ADC0. When EXT_CLK is enabled, ADC channel will not work and DIDR0 will not disable the digital input buffer.
When both PCINT and the corresponding ADC channel are enabled, the digital input buffer will not be disabled.
When ACO is enabled, ADC, TC and USART RX inputs are not disabled.
When OC0B is enabled, ADC and AC will continue to receive inputs on that channel if enabled.
When CLKO is enable in PB[1], OCA will get lower priority.
When USART is enabled, the users must ensure that ADC channel corresponding to the TxD0 pin is not used. Because DIDR0 register will only control the input buffer, not the output part.
During reset/external programming, all pins are treated as inputs and outputs are disabled.
Alternative location when enabling T/C Remap

8-bit AVR Microcontroller

6 I/O Multiplexing