Datasheet
ATmega164A/PA/324A/PA/644A/PA/1284/P
2018 Microchip Technology Inc. Data Sheet Complete DS40002070A-page 95
• OC1B/XCK1/PCINT28 – Port D, Bit 4
OC1B, Output Compare Match B output: The PB4 pin can serve as an external output for the Timer/Counter1
Output Compare B. The pin has to be configured as an output (DDD4 set (one)) to serve this function. The
OC1B pin is also the output pin for the PWM mode timer function.
XCK1, USART1 External clock. The Data Direction Register (DDB4) controls whether the clock is output (DDD4
set “one”) or input (DDD4 cleared). The XCK4 pin is active only when the USART1 operates in Synchronous
mode.
PCINT28, Pin Change Interrupt Source 28: The PD4 pin can serve as an external interrupt source.
• INT1/TXD1/PCINT27 – Port D, Bit 3
INT1, External Interrupt source 1. The PD3 pin can serve as an external interrupt source to the MCU.
TXD1, Transmit Data (Data output pin for the USART1). When the USART1 Transmitter is enabled, this pin is
configured as an output regardless of the value of DDD3.
PCINT27, Pin Change Interrupt Source 27: The PD3 pin can serve as an external interrupt source.
• INT0/RXD1/PCINT26 – Port D, Bit 2
INT0, External Interrupt source 0. The PD2 pin can serve as an external interrupt source to the MCU.
RXD1, RXD0, Receive Data (Data input pin for the USART1). When the USART1 receiver is enabled this pin is
configured as an input regardless of the value of DDD2. When the USART forces this pin to be an input, the
pull-up can still be controlled by the PORTD2 bit.
PCINT26, Pin Change Interrupt Source 26: The PD2 pin can serve as an external interrupt source.
• TXD0/PCINT25 – Port D, Bit 1
TXD0, Transmit Data (Data output pin for the USART0). When the USART0 Transmitter is enabled, this pin is
configured as an output regardless of the value of DDD1.
PCINT25, Pin Change Interrupt Source 25: The PD1 pin can serve as an external interrupt source.
• RXD0/T3/PCINT24 – Port D, Bit 0
RXD0, Receive Data (Data input pin for the USART0). When the USART0 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.
T3, Timer/Counter3 counter source (only for ATmega1284/1284P).
PCINT24, Pin Change Interrupt Source 24: The PD0 pin can serve as an external interrupt source.
Table 14-13 on page 96 and Table 14-14 on page 96 relate the alternate functions of Port D to the overriding
signals shown in Figure 14-5 on page 85.