Programming Arduino Getting Started with Sketches

setup
function of this sketch:
Figure 7-4
Types of interrupt signals
The first argument specifies which of the two interrupts you want to use. Rather
confusingly, a 0 here means you are using pin 2, while a 1 means you are using pin 3.

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The next argument is the name of the function that is to be called when there is an
interrupt, and the final argument is a constant that will be one of 
CHANGE, RISING
, or
FALLING
. 
Figure 7-4
summarizes these options.
If the interrupt mode is CHANGE, then either a RISING from 0 to 1 or a FALLING
from 1 to 0 will both trigger an interrupt.
You can disable interrupts using the function 
noInterrupts
. This stops all interrupts
from both interrupt channels. You can resume using interrupts again by calling the
function 
interrupts
.
Conclusion
In this chapter, you have looked at some of the handy features that the Arduino standard
library provides. These features will save you some programming effort, and if there is
one thing that a good programmer likes, it is being able to use high-quality work done by
other people.
In the next chapter, we will extend what we learned about data structures in 
Chapter 5
and look at how you go about remembering data on the Arduino after the power goes off.

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8
Data Storage
When you
give values to variables, the Arduino board will remember those values only as
long as the power is on. The moment that you turn the power off or reset the board, all that
data is lost.
In this chapter, we look at some ways to hang on to that data.
Constants
If the data that you want to store does not change, then you can just set the data up each
time that the Arduino starts. An example of this approach is the case in the letters array in
your Morse code translator of 
Chapter 5
(sketch 5-05).
You used the following code to define a variable of the correct size and fill it with the
data that you needed:
You may remember that you did the calculation and decided that you had plenty of your
meager 2K to spare. However, if memory was a bit tight, it would be far better to be able
to store this data in the 32K of flash memory used to store programs, rather than the 2K of
RAM. There is a means of doing this. It is a directive called