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This document covers the configuration and usage of Pin Change Interrupt 1 (PCINT1) on the ATmega328 microcontroller. It explains how to enable interrupts for pins PC0–PC5 using PCICR and PCMSK1, how to clear the PCIF1 flag, write the ISR, and implement logic to detect pin changes.

PCINT1 Overview

Group Pins Port Interrupt Vector
PCINT1 PC0–PC5 PORTC PCINT1_vect

Pin Change Interrupt 1 monitors all pins on PORTC. Any logical change (rising or falling edge) on an enabled pin will trigger the interrupt.

PCICR – Pin Change Interrupt Control Register

Bit Name Description
1 PCIE1 Enable Pin Change Interrupt for PCINT1 group

Enable PCINT1 Group:

bitSet(PCICR, PCIE1); // Enable pin change interrupt for PORTC (PCINT1 group)

PCMSK1 – Pin Change Mask Register 1 (Port C)

Bit Name Pin Description
0 PCINT8 PC0 Enable pin change interrupt for PC0
1 PCINT9 PC1 Enable pin change interrupt for PC1
2 PCINT10 PC2 Enable pin change interrupt for PC2
3 PCINT11 PC3 Enable pin change interrupt for PC3
4 PCINT12 PC4 Enable pin change interrupt for PC4
5 PCINT13 PC5 Enable pin change interrupt for PC5

Enable Interrupts for Port C Pins (Examples)

bitSet(PCMSK1, PCINT8);  // Enable interrupt for PC0
bitSet(PCMSK1, PCINT9);  // Enable interrupt for PC1
bitSet(PCMSK1, PCINT10); // Enable interrupt for PC2
bitSet(PCMSK1, PCINT11); // Enable interrupt for PC3
bitSet(PCMSK1, PCINT12); // Enable interrupt for PC4
bitSet(PCMSK1, PCINT13); // Enable interrupt for PC5

You can enable multiple pins simultaneously by setting multiple bits.

PCMSK1 |= (1 << PCINT9) | (1 << PCINT11); // Enable PC1 and PC3

PCIFR – Pin Change Interrupt Flag Register

Bit Name Description
1 PCIF1 Pin Change Interrupt Flag for PCINT1

Clear PCINT1 Flag Manually:

intFlag_clear(PCIFR, PCIF1); // Clear PCINT1 interrupt flag

Note

The flag is automatically cleared when the ISR is executed.

Writing the ISR for PCINT1

The ISR is triggered on any logical change of enabled pins in PORTC. You must read the current pin state and compare it to the previous state to detect rising or falling edges.

Example ISR:

ISR(PCINT1_vect) 
{
    if (bitCheckHigh(PINC, 2)) 
    {
        // Rising edge on PC2
    } 
    else 
    {
        // Falling edge on PC2
    }
}

Complete Initialization Example

void pcint1_Init(void) 
{
    GPIO_Config_INPUT(DDRC, PC2);     // Configure PC2 as input
    bitSet(PCICR, PCIE1);             // Enable PCINT1 group
    bitSet(PCMSK1, PCINT10);          // Enable interrupt for PC2
    globalInt_Enable;                 // Enable global interrupts
}

Summary of PCINT1 Setup

Step Register Action
Configure PCx as input DDRC GPIO_Config_INPUT(DDRC, PCx)
Enable PCINTx in mask PCMSK1 Set PCINTx bit
Enable PCINT1 group PCICR Set PCIE1 bit
Enable global interrupts SREG Set SREG_I bit
Write ISR PCINT1_vect Detect and handle pin changes

Caution

Pin change interrupts are edge-agnostic. You must track previous pin states to determine rising or falling edges.

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