Possibility to use an alternative InteruptPin (IRQ) on Arduino Mega 2560

Added by Alban_T 30 days ago


I ran into a slight unforseen problem in my project.
I'm using an Arduino Mega 2560 in conjunction with the RFM12B Board and got it working without any problems until I attached my GLCD shield :(
It appears that both my RFM12B board and the GLCD are trying to use the same interupt pin (IRQ a.k.a. pin 2).

I found thru my precious friend Google that it is possible to change the IRQ pin that the Jeelib is using by editing RF12.cpp.

// pin change interrupts are currently only supported on ATmega328's
// #define PINCHG_IRQ 1    // uncomment this to use pin-change interrupts

// maximum transmit / receive buffer: 3 header + data + 2 crc bytes
#define RF_MAX   (RF12_MAXDATA + 5)

// pins used for the RFM12B interface - yes, there *is* logic in this madness:
//  - leave RFM_IRQ set to the pin which corresponds with INT0, because the
//    current driver code will use attachInterrupt() to hook into that
//  - (new) you can now change RFM_IRQ, if you also enable PINCHG_IRQ - this
//    will switch to pin change interrupts instead of attach/detachInterrupt()
//  - use SS_DDR, SS_PORT, and SS_BIT to define the pin you will be using as
//    select pin for the RFM12B (you're free to set them to anything you like)
//  - please leave SPI_SS, SPI_MOSI, SPI_MISO, and SPI_SCK as is, i.e. pointing
//    to the hardware-supported SPI pins on the ATmega, *including* SPI_SS !

#if defined(__AVR_ATmega2560__) || defined(__AVR_ATmega1280__)

#define RFM_IRQ     2
#define SS_DDR      DDRB
#define SS_PORT     PORTB
#define SS_BIT      0

#define SPI_SS      53    // PB0, pin 19
#define SPI_MOSI    51    // PB2, pin 21
#define SPI_MISO    50    // PB3, pin 22
#define SPI_SCK     52    // PB1, pin 20

Unfortunately there is also a comment in here that it only works for ATmega328 :(
On the Mega I have several interupt pins free (18 to 21 a.k.a. INT3, 2 1 and 0) so I'm hoping to be able to use one of these.
I wasn't able to get it to work so I hope someone here could give me some advise.

Thanks in advance,


Replies (1)

RE: Possibility to use an alternative InteruptPin (IRQ) on Arduino Mega 2560 - Added by JohnO 15 days ago

Did we miss this one? Did you get to a resolution Alban?