I had a very hard time figuring out how to use Pin-Change Interrupts. I found AVR documentation hard to follow, and Arduino libraries overly complicated and obfuscating. Here is an example of how to use pin-change interrupts for Arduino (mega). It may help.
PCICR |= 1; // enable PCI0 pin group interrupt
PCMSK0 |= 0b1100; // enable PC interrupts on arduino pins 50,51, which are in group PCI0
/// Pin-Change interrupt, for group PCI0 (arduino mega pins 13..10, and 50..53)
// do what you need to do when one of the pins in this group changes.
// usually... check to see which pin changed here... then do something.
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