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Diffstat (limited to 'source/arduino/constants.rst')
| -rw-r--r-- | source/arduino/constants.rst | 189 |
1 files changed, 173 insertions, 16 deletions
diff --git a/source/arduino/constants.rst b/source/arduino/constants.rst index 49f3933..b082774 100644 --- a/source/arduino/constants.rst +++ b/source/arduino/constants.rst @@ -7,26 +7,29 @@ Constants are predefined variables in the Arduino language. They are used to make the programs easier to read. We classify constants in groups. +.. contents:: Contents + :local: +.. _arduino-constants-bool: -Defining Logical Levels, true and false (Boolean Constants) -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Boolean Constants +----------------- There are two constants used to represent truth and falsity in the Arduino language: **true**, and **false**. - +.. _arduino-constants-false: false ------ +^^^^^ false is the easier of the two to define. false is defined as 0 (zero). - +.. _arduino-constants-true: true ----- +^^^^ true is often said to be defined as 1, which is correct, but true has a wider definition. Any integer which is *non-zero* is TRUE, in @@ -34,19 +37,17 @@ a Boolean sense. So -1, 2 and -200 are all defined as true, too, in a Boolean sense. - Note that the *true* and *false* constants are typed in lowercase unlike HIGH, LOW, INPUT, & OUTPUT. - Defining Pin Levels, HIGH and LOW -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +--------------------------------- When reading or writing to a digital pin there are only two possible values a pin can take/be-set-to: **HIGH** and **LOW**. - +.. _arduino-constants-high: **HIGH** @@ -73,7 +74,7 @@ with digitalWrite, the pin is at 5 volts. In this state it can series resistor to ground, or to another pin configured as an output, and set to LOW. - +.. _arduino-constants-low: **LOW** @@ -96,7 +97,7 @@ output, and set to HIGH. Defining Digital Pins, INPUT and OUTPUT -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +--------------------------------------- Digital pins can be used either as **INPUT** or **OUTPUT**. Changing a pin from INPUT TO OUTPUT with pinMode() drastically @@ -105,7 +106,7 @@ changes the electrical behavior of the pin. Pins Configured as Inputs -------------------------- +^^^^^^^^^^^^^^^^^^^^^^^^^ Arduino (Atmega) pins configured as **INPUT** with pinMode() are said to be in a high-impedance state. One way of explaining this is @@ -117,7 +118,7 @@ reading a sensor, but not powering an LED. Pins Configured as Outputs --------------------------- +^^^^^^^^^^^^^^^^^^^^^^^^^^ Pins configured as **OUTPUT** with pinMode() are said to be in a low-impedance state. This means that they can provide a substantial @@ -131,6 +132,158 @@ of current provided by an Atmega pin is also not enough to power most relays or motors, and some interface circuitry will be required. +.. _arduino-fpconstants: + +Floating-Point Constants +------------------------ + +Similar to integer constants, floating point constants are used to +make code more readable. Floating point constants are swapped at +compile time for the value to which the expression evaluates. + + + +Examples: + + + +``n = .005;`` + + + +Floating point constants can also be expressed in a variety of +scientific notation. 'E' and 'e' are both accepted as valid +exponent indicators. + + + +:: + + + floating-point evaluates to: also evaluates to: + constant + + 10.0 10 + 2.34E5 2.34 * 10^5 234000 + 67e-12 67.0 * 10^-12 .000000000067 + +.. _arduino-constants-integers: + +Integer Constants +----------------- + +Integer constants are numbers used directly in a sketch, like +``123``. By default, these numbers are treated as +`int <http://arduino.cc/en/Reference/Int>`_'s but you can change +this with the U and L modifiers (see below). + + + +Normally, integer constants are treated as base 10 (decimal) +integers, but special notation (formatters) may be used to enter +numbers in other bases. + + + +:: + + Base Example Formatter Comment + + 10 (decimal) 123 none + + 2 (binary) B1111011 leading 'B' only works with 8 bit values (0 to 255) + characters 0-1 valid + + 8 (octal) 0173 leading "0" characters 0-7 valid + + 16 (hexadecimal) 0x7B leading "0x" characters 0-9, A-F, a-f valid + +.. _arduino-constants-integers-dec: + +**Decimal** is base 10. This is the common-sense math with which +you are acquainted. Constants without other prefixes are assumed to +be in decimal format. + + + +Example: +:: + + 101 // same as 101 decimal ((1 * 10^2) + (0 * 10^1) + 1) + +.. _arduino-constants-integers-bin: + +**Binary** is base two. Only characters 0 and 1 are valid. + + + +Example: +:: + + B101 // same as 5 decimal ((1 * 2^2) + (0 * 2^1) + 1) + +The binary formatter only works on bytes (8 bits) between 0 (B0) +and 255 (B11111111). If it is convenient to input an int (16 bits) +in binary form you can do it a two-step procedure such as: + + + +:: + + myInt = (B11001100 * 256) + B10101010; // B11001100 is the high byte + +.. _arduino-constants-integers-oct: + +**Octal** is base eight. Only characters 0 through 7 are valid. Octal +values are indicated by the prefix "0". + +Example: + +:: + + 0101 // same as 65 decimal ((1 * 8^2) + (0 * 8^1) + 1) + +Warning +It is possible to generate a hard-to-find bug by (unintentionally) +including a leading zero before a constant and having the compiler +unintentionally interpret your constant as octal. + +.. _arduino-constants-integers-hex: + +**Hexadecimal (or hex)** is base sixteen. Valid characters are 0 +through 9 and letters A through F; A has the value 10, B is 11, up +to F, which is 15. Hex values are indicated by the prefix "0x". +Note that A-F may be syted in upper or lower case (a-f). + + + +Example: + +:: + + 0x101 // same as 257 decimal ((1 * 16^2) + (0 * 16^1) + 1) + +.. _arduino-constants-integers-u-l: + +U & L formatters +^^^^^^^^^^^^^^^^ + +By default, an integer constant is treated as an +`int <http://arduino.cc/en/Reference/Int>`_ with the attendant +limitations in values. To specify an integer constant with another +data type, follow it with: + + + + +- a 'u' or 'U' to force the constant into an unsigned data format. + Example: ``33u`` +- a 'l' or 'L' to force the constant into a long data format. + Example: ``100000L`` +- a 'ul' or 'UL' to force the constant into an unsigned long + constant. Example: ``32767ul`` + + See also @@ -140,5 +293,9 @@ See also - `pinMode() <http://arduino.cc/en/Reference/PinMode>`_ - `Integer Constants <http://arduino.cc/en/Reference/IntegerConstants>`_ - `boolean variables <http://arduino.cc/en/Reference/BooleanVariables>`_ - - +- `#define <http://arduino.cc/en/Reference/Define>`_ +- `byte <http://arduino.cc/en/Reference/Byte>`_ +- `int <http://arduino.cc/en/Reference/Int>`_ +- `unsigned int <http://arduino.cc/en/Reference/UnsignedInt>`_ +- `long <http://arduino.cc/en/Reference/Long>`_ +- `unsigned long <http://arduino.cc/en/Reference/UnsignedLong>`_ |