Alternate Functions of Port A

The Port A pins with alternate functions are shown in the table below:

Table 1. Port A Pins Alternate Functions
Port Pin	Alternate Functions
PA[0]	ADC0: ADC Input Channel 0 AIN0: Analog Comparator, Positive Input T0: Timer/Counter0 Clock Source (default location) PCINT0: Pin Change Interrupt source 0 CLKI: External Clock TPICLK: Serial Programming Clock
PA[1]	ADC1: ADC Input Channel 1 AIN1: Analog Comparator, Negative Input OC0B: Timer/Counter0 Compare Match B Output (default location) PCINT1: Pin Change Interrupt source 1 TPIDATA: Serial Programming Data
PA[2]	PCINT2: Pin Change Interrupt source 2 RESET: Reset Pin
PA[3]	OC0A: Timer/Counter0 Compare Match A Output (alternative location) PCINT3: Pin Change Interrupt source 3
PA[4]	ICP0: Timer/Counter0 Input Capture Input (alternative location) PCINT4: Pin Change Interrupt source 4
PA[5]	ADC2: ADC Input Channel 2 OC0B: Timer/Counter0 Compare Match B Output (alternative location) PCINT5: Pin Change Interrupt source 5
PA[6]	ADC3: ADC Input Channel 3 PCINT6: Pin Change Interrupt source 6
PA[7]	PCINT7: Pin Change Interrupt source 7

The alternate pin configuration is as follows:

PA[0] – ADC0/AIN0/T0/PCINT0/CLKI/TPICLK
- ADC0: Analog to Digital Converter, Channel 0.
- AIN0: Analog Comparator Positive Input. Configure the port pin as input with the internal pull-up switched off to avoid the digital port function from interfering with the function of the Analog Comparator.
- T0: Timer/Counter0 counter source.
- PCINT0: Pin Change Interrupt source 0. The PA[0] pin can serve as an external interrupt source for pin change interrupt 0.
- CLKI: External Clock.
- TPICLK: Serial Programming Clock.
PA[1] – ADC1/AIN1/OC0B/PCINT1/TPIDATA
- ADC1: Analog to Digital Converter, Channel 1.
- AIN1: Analog Comparator Negative Input. Configure the port pin as input with the internal pull-up switched off to avoid the digital port function from interfering with the function of the Analog Comparator.
- OC0B: Output Compare Match B Output. The PA[1] pin can serve as an external output for the Timer/Counter0 Compare Match B. The PA[1] pin has to be configured as an output (DDB1 set (one)) to serve this function. The OC0B pin is also the output pin for the PWM mode timer function.
- PCINT1: Pin Change Interrupt source 1. The PA[1] pin can serve as an external interrupt source for pin change interrupt 0.
- TPIDATA: Serial Programming Data.
PA[2] – PCINT2/RESET
- PCINT2: Pin Change Interrupt source 2. The PA[2] pin can serve as an external interrupt source for pin change interrupt 0.
- RESET: Reset Pin.
PA[3] – OC0A/PCINT3
- OC0A: Output Compare Match A Output. The PA[3] pin can serve as an external output for the Timer/Counter0 Compare Match A. The pin has to be configured as an output (DDB0 set (one)) to serve this function. This is also the output pin for the PWM mode timer function.
- PCINT3: Pin Change Interrupt source 3. The PA[3] pin can serve as an external interrupt source for pin change interrupt 0.
PA[4] - ICP0/PCINT4
- ICP0: Input Capture Pin. The PA[4] pin can act as an Input Capture pin for Timer/Counter0.
- PCINT4: Pin Change Interrupt source 4. The PA4 pin can serve as an external interrupt source for pin change interrupt 0.
PA[5] - ADC2/OC0B/PCINT5
- ADC2: Analog to Digital Converter, Channel 2.
- OC0B: Output Compare Match B Output: The PA1 pin can serve as an external output for the Timer/Counter0 Compare Match B. The PA[5] pin has to be configured as an output (DDB1 set (one)) to serve this function. The OC0B pin is also the output pin for the PWM mode timer function.
- PCINT5: Pin Change Interrupt source 5. The PA5 pin can serve as an external interrupt source for pin change interrupt 0.
PA[6] - ADC3/PCINT6
- ADC3: Analog to Digital Converter, Channel 3.
- PCINT6: Pin Change Interrupt source 6. The PA6 pin can serve as an external interrupt source for pin change interrupt 0.
PA[7] - PCINT7
- PCINT7: Pin Change Interrupt source 7. The PA7 pin can serve as an external interrupt source for pin change interrupt 0.

The following tables relate the alternate functions of Port B to the overriding signals shown in the figure of Alternate Port Functions.

Table 2. Overriding Signals for Alternate Functions in PA[7:6]
Signal  Name	PA7/PCINT7	PA6/ADC3/PCINT6
PUOE	0	0
PUOV	0	0
DDOE	0	0
DDOV	0	0
PVOE	0	0
PVOV	0	0
PTOE	0	0
DIEOE	(PCINT7 • PCIE0)	(PCINT6 • PCIE0) + ADC3D
DIEOV	PCINT7 • PCIE0	PCINT6 • PCIE0
DI	PCINT7 Input	PCINT6 input
AIO	-	ADC3

Table 3. Overriding Signals for Alternate Functions in PA[5:4]
Signal  Name	PA5/ADC2/OC0B/PCINT5	PA4/ICP0/PCINT4
PUOE	0	0
PUOV	0	0
DDOE	0	0
DDOV	0	0
PVOE	(OC0B Enable • REMAP)	0
PVOV	(OC0B • REMAP)	0
PTOE	0	0
DIEOE	(PCINT5 • PCIE0) + ADC2D	(PCINT4 • PCIE0)
DIEOV	PCINT5 • PCIE0	(PCINT4 • PCIE0)
DI	PCINT5 Input	ICP0/PCINT4 Input
AIO	ADC2	-

Table 4. Overriding Signals for Alternate Functions in PA[3:2]
Signal  Name	PA3/OC0A/PCINT3	PA4/ICP0/PCINT4
PUOE	0	RSTDISBL⁽¹⁾
PUOV	0	1
DDOE	0	RSTDISBL⁽¹⁾
DDOV	0	0
PVOE	(OC0A Enable • REMAP)	0
PVOV	(OC0A • REMAP)	0
PTOE	0	0
DIEOE	(PCINT3 • PCIE0)	RSTDISBL⁽¹⁾ + (PCINT2 • PCIE0)
DIEOV	PCINT3 • PCIE0	RSTDISBL • PCINT2 • PCIE0
DI	PCINT3 Input	PCINT2 input
AIO	-	-

Note:

RSTDISBL is 1 when the configuration bit is “0” (Programmed).

Table 5. Overriding Signals for Alternate Functions in PA[1:0]
Signal  Name	PA1/ADC1/AIN1/OC0B/PCINT1	PA0/ADC0/AIN0/CLKI/T0/PCINT0
PUOE	0	EXT_CLOCK⁽¹⁾
PUOV	0	0
DDOE	0	EXT_CLOCK⁽¹⁾
DDOV	0	0
PVOE	(OC0B Enable • REMAP)	EXT_CLOCK⁽¹⁾
PVOV	(OC0B • REMAP)	0
PTOE	0	0
DIEOE	(PCINT1 • PCIE0) + ADC1D	EXT_CLOCK⁽¹⁾ + (PCINT0 • PCIE0) + ADC0D
DIEOV	PCINT1 • PCIE0	EXT_CLOCK⁽¹⁾• PWR_DOWN) + (EXT_CLOCK⁽¹⁾• PCINT0 • PCIE0)
DI	PCINT1 Input	CLKI/T0/PCINT0 Input
AIO	ADC1/Analog Comparator Negative Input	ADC0/Analog Comparator Positive Input

Note:

EXT_CLOCK is 1 when external clock is selected as main clock.