The Arduino Language - Arduino Sketches: Tools and Techniques for Programming Wizardry - page 65

CHAPTER
4
The Arduino Language
Functionality can be added to Arduino programs using libraries, but every
Arduino project invariably starts with one library; the Arduino Language. The
Arduino Language contains everything required for basic programs, allowing
access to input and output pins, mathematical functions, and control structures.
This chapter lists those functions and gives an explanation of each one. You can
also consult the Arduino reference page at http://arduino.cc/en/Reference/ .
I/O Functions
An Arduino is a powerful system, but its power comes from interacting with the
real world. To do this, the Arduino must use Input and Output, shortened to I/O.
Pins can be dei ned as either being an input or output; it is up to you to decide.
Digital I/O
Digital I/O is dei ned as using a digital signal to communicate; a logical 1 or
logical 0. In Arduino, 1 is dei ned as having a “high” voltage; normally at or
close to the system voltage. 0 is dei ned as having a “low” voltage, typically 0.
A system powered by 5 volts will usually have 5 volts for a logical 1 and 0 volt
for a logical 0. A system powered by 3.3 V will usually have 3.3 V and 0.