So, This is your code slightly altered. I am using it to read the readings of the roll and pitch of a quadcopter. I have tried using this code for a mega 2560 but it does not work in ports A0 and A1. I think it might in A5 and A6 but I am unsure how to alter this code. THank you, Rohan Paleja

/*  rcTiming.ino -- JW, 30 November 2015 -- 
 * Uses pin-change interrupts on A0-A4 to time RC pulses
 * Ref: http://arduino.stackexchange.com/questions/18183/read-rc-receiver-channels-using-interrupt-instead-of-pulsein

#include <Streaming.h>
static   byte rcOld;        // Prev. states of inputs
volatile unsigned long rcRises[2]; // times of prev. rising edges
volatile unsigned long rcTimes[2]; // recent pulse lengths
volatile unsigned int  rcChange=0; // Change-counter
int Roll, Pitch;
// Be sure to call setup_rcTiming() from setup()
void setup_rcTiming() {
  rcOld = 0;
  pinMode(A0, INPUT);  // pin 14, A0, PC0, for pin-change interrupt
  pinMode(A1, INPUT);  // pin 15, A1, PC1, for pin-change interrupt

  PCMSK1 |= 0x0F;       // Four-bit mask for four channels
  PCIFR  |= 0x02;       // clear pin-change interrupts if any
  PCICR  |= 0x02;       // enable pin-change interrupts
// Define the service routine for PCI vector 1
ISR(PCINT1_vect) {
  byte rcNew = PINC & 15;   // Get low 4 bits, A0-A3
  byte changes = rcNew^rcOld;   // Notice changed bits
  byte channel = 0;
  unsigned long now = micros(); // micros() is ok in int routine
  while (changes) {
    if ((changes & 1)) {  // Did current channel change?
      if ((rcNew & (1<<channel))) { // Check rising edge
        rcRises[channel] = now;     // Is rising edge
      } else {              // Is falling edge
        rcTimes[channel] = now-rcRises[channel];
    changes >>= 1;      // shift out the done bit
  rcOld = rcNew;        // Save new state

void setup() {
  Serial.println("Starting RC Timing Test");

void loop() {
  unsigned long rcT[2]; // copy of recent pulse lengths
  unsigned int rcN;
  if (rcChange) {

    // Data is subject to races if interrupted, so off interrupts
    cli();          // Disable interrupts
    rcN = rcChange;
    rcChange = 0;       // Zero the change counter
    Roll = rcTimes[0];
    Pitch = rcTimes[1];

    sei();          // reenable interrupts

    Serial <<  " " << Roll << " " << Pitch
       << " "  << rcN << endl;

  sei();            // reenable interrupts

1 Answer 1


You are trying to do an Pin Change Interrupt on Port F (A0-A7). On the arduino Uno, this port does support PCINT but not on the Arduino Mega.

An option is to use the Port K for the PCINT. Instead of A0 and A1 you then use A8 and A9. A few little changes in the code should do the job:

void setup_rcTiming() {
rcOld = 0;
pinMode(A8, INPUT);  // pin 14, A0, PC0, for pin-change interrupt
pinMode(A9, INPUT);  // pin 15, A1, PC1, for pin-change interrupt

PCMSK2 |= 0x0F;       // Four-bit mask for four channels
PCIFR  |= 0x04;       // clear pin-change interrupts if any
PCICR  |= 0x04;       // enable pin-change interrupts


ISR(PCINT2_vect) {
byte rcNew = PINK & 15;
  • I have tried this code. It still does not work. I changed the code, and plugged my signal from the receiver into A8 and A9 and no readings are being read through my serial read. Do you know why this code still isn't working? @Janw Jul 7, 2016 at 16:03
  • I did edit the code because I made a mistake. In PCIFR and PCICR bit 3 should be set and not bit 2.
    – Janw
    Jul 7, 2016 at 16:29
  • If I was to use A9 and A12 or A10 and A11 would I have to change anything other than pinmode? @Janw Jul 11, 2016 at 15:56
  • If you want to use the pins you mention, you should change the value of PCMSK2. In this register you can set the pins you want to use. It takes any byte or you can set each bit separately. The least significant bit corresponds with A8, the most significant bit with A15. You can find more info about this in the datasheet of the atmega2560. Its in chapter 15 (external interrupts). PCMSK2 is on page 113.
    – Janw
    Jul 11, 2016 at 16:18

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.