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diff --git a/docs/source/arduino/constants.rst b/docs/source/arduino/constants.rst deleted file mode 100644 index e841c9b..0000000 --- a/docs/source/arduino/constants.rst +++ /dev/null @@ -1,302 +0,0 @@ -.. _arduino-constants: - -constants -========= - -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: - -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 -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** - - - -The meaning of HIGH (in reference to a pin) is somewhat different -depending on whether a pin is set to an INPUT or OUTPUT. When a pin -is configured as an INPUT with pinMode, and read with digitalRead, -the microcontroller will report HIGH if a voltage of 3 volts or -more is present at the pin. - - - -A pin may also be configured as an INPUT with pinMode, and -subsequently made HIGH with digitalWrite, this will set the -internal 20K pullup resistors, which will *steer* the input pin to -a HIGH reading unless it is pulled LOW by external circuitry. - - - -When a pin is configured to OUTPUT with pinMode, and set to HIGH -with digitalWrite, the pin is at 5 volts. In this state it can -*source* current, e.g. light an LED that is connected through a -series resistor to ground, or to another pin configured as an -output, and set to LOW. - -.. _arduino-constants-low: - -**LOW** - - - -The meaning of LOW also has a different meaning depending on -whether a pin is set to INPUT or OUTPUT. When a pin is configured -as an INPUT with pinMode, and read with digitalRead, the -microcontroller will report LOW if a voltage of 2 volts or less is -present at the pin. - - - -When a pin is configured to OUTPUT with pinMode, and set to LOW -with digitalWrite, the pin is at 0 volts. In this state it can -*sink* current, e.g. light an LED that is connected through a -series resistor to, +5 volts, or to another pin configured as an -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 -changes the electrical behavior of the pin. - -.. _arduino-constants-input: - -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 -that pins configured as INPUT make extremely small demands on the -circuit that they are sampling, say equivalent to a series resistor -of 100 Megohms in front of the pin. This makes them useful for -reading a sensor, but not powering an LED. - -.. _arduino-constants-output: - -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 -amount of current to other circuits. Atmega pins can source -(provide positive current) or sink (provide negative current) up to -40 mA (milliamps) of current to other devices/circuits. This makes -them useful for powering LED's but useless for reading sensors. -Pins configured as outputs can also be damaged or destroyed if -short circuited to either ground or 5 volt power rails. The amount -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-constants-fp: - -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. - -.. TODO explain that floating point literals are doubles - -.. _arduino-constants-fp-f: - -.. TODO f modifiers - -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 --------- - - -- `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>`_ - - -.. include:: cc-attribution.txt |