The attached NANO pinout chart shows two types of pins that look like interrupts.
It shows INT0 and INT1 in pink with the label “Interrupt Pin”
It also shows a bunch of PCINTn pins in white with the label “INT”
What’s the difference?
What I need is a NANO input pin that will be set to generate an interrupt whenever the external device changes that pin’s state.
The old ATmega8 had only INT0 and INT1.
To add more interrupts, they have added another layer of interrupts, called "pin change interrupt" or "PCINT". Almost every pin of the ATmega328P can be used as "PCINT".
The Arduino libraries support the INT0 and INT1, but not the PCINT yet.
There is a good library for the PCINT : GitHub - GreyGnome/EnableInterrupt: New Arduino interrupt library, designed for Arduino Uno/Mega 2560/Leonardo/Due
Ok, thanks to both of you.