Alternate Functions of Port D

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

Table 1. Port D Pins Alternate Functions
Port Pin	Alternate Function
PD7	AIN1 (Analog Comparator Negative Input)
PD6	AIN0 (Analog Comparator Positive Input)
PD5	T1 (Timer/Counter 1 External Counter Input)
PD4	XCK (USART External Clock Input/Output) T0 (Timer/Counter 0 External Counter Input)
PD3	INT1 (External Interrupt 1 Input)
PD2	INT0 (External Interrupt 0 Input)
PD1	TXD (USART Output Pin)
PD0	RXD (USART Input Pin)

The alternate pin configuration is as follows:

• AIN1 – Port D, Bit 7

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.

• AIN0 – Port D, Bit 6

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.

• T1 – Port D, Bit 5

T1, Timer/Counter1 counter source.

• XCK/T0 – Port D, Bit 4

XCK, USART external clock.

T0, Timer/Counter0 counter source.

• INT1 – Port D, Bit 3

INT1, External Interrupt source 1: The PD3 pin can serve as an external interrupt source.

• INT0 – Port D, Bit 2

INT0, External Interrupt source 0: The PD2 pin can serve as an external interrupt source.

• TXD – Port D, Bit 1

TXD, Transmit Data (Data output pin for the USART). When the USART Transmitter is enabled, this pin is configured as an output regardless of the value of DDD1.

• RXD – Port D, Bit 0

RXD, Receive Data (Data input pin for the USART). When the USART Receiver is enabled this pin is configured as an input regardless of the value of DDD0. When the USART forces this pin to be an input, the pull-up can still be controlled by the PORTD0 bit.

The tables below relate the alternate functions of Port D to the overriding signals shown in figure Figure 1.

Table 2. Overriding Signals for Alternate Functions PD7:PD4
Signal Name	PD7/AIN1	PD6/AIN0	PD5/T1	PD4/XCK/ T0
PUOE	0	0	0	0
PUO	0	0	0	0
OOE	0	0	0	0
OO	0	0	0	0
PVOE	0	0	0	UMSEL
PVO	0	0	0	XCK OUTPUT
DIEOE	0	0	0	0
DIEO	0	0	0	0
DI	–	–	T1 INPUT	XCK INPUT / T0 INPUT
AIO	AIN1 INPUT	AIN0 INPUT	–	–

Table 3. Overriding Signals for Alternate Functions in PD3:PD0
Signal Name	PD3/INT1	PD2/INT0	PD1/TXD	PD0/RXD
PUOE	0	0	TXEN	RXEN
PUO	0	0	0	PORTD0 • PUD
OOE	0	0	TXEN	RXEN
OO	0	0	1	0
PVOE	0	0	TXEN	0
PVO	0	0	TXD	0
DIEOE	INT1 ENABLE	INT0 ENABLE	0	0
DIEO	1	1	0	0
DI	INT1 INPUT	INT0 INPUT	–	RXD
AIO	–	–	–	–

8-bit AVR Microcontroller

Alternate Functions of Port D