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+.. _arduino-bitwiseand:
+
+Bitwise AND (&), Bitwise OR (\|), Bitwise XOR (^)
+=================================================
+
+Bitwise AND (&)
+---------------
+
+The bitwise operators perform their calculations at the bit level
+of variables. They help solve a wide range of common programming
+problems. Much of the material below is from an excellent tutorial
+on bitwise math wihch may be found
+`here. <http://www.arduino.cc/playground/Code/BitMath>`_
+
+
+
+Description and Syntax
+----------------------
+
+Below are descriptions and syntax for all of the operators. Further
+details may be found in the referenced tutorial.
+
+
+
+Bitwise AND (&)
+---------------
+
+The bitwise AND operator in C++ is a single ampersand, &, used
+between two other integer expressions. Bitwise AND operates on each
+bit position of the surrounding expressions independently,
+according to this rule: if both input bits are 1, the resulting
+output is 1, otherwise the output is 0. Another way of expressing
+this is:
+
+
+
+::
+
+        0  0  1  1    operand1
+        0  1  0  1    operand2
+        ----------
+        0  0  0  1    (operand1 & operand2) - returned result
+
+
+
+In Arduino, the type int is a 16-bit value, so using & between two
+int expressions causes 16 simultaneous AND operations to occur. In
+a code fragment like:
+
+
+
+::
+
+        int a =  92;    // in binary: 0000000001011100
+        int b = 101;    // in binary: 0000000001100101
+        int c = a & b;  // result:    0000000001000100, or 68 in decimal.
+
+
+
+Each of the 16 bits in a and b are processed by using the bitwise
+AND, and all 16 resulting bits are stored in c, resulting in the
+value 01000100 in binary, which is 68 in decimal.
+
+
+
+One of the most common uses of bitwise AND is to select a
+particular bit (or bits) from an integer value, often called
+masking. See below for an example
+
+
+
+Bitwise OR (\|)
+---------------
+
+The bitwise OR operator in C++ is the vertical bar symbol, \|. Like
+the & operator, \| operates independently each bit in its two
+surrounding integer expressions, but what it does is different (of
+course). The bitwise OR of two bits is 1 if either or both of the
+input bits is 1, otherwise it is 0. In other words:
+
+
+
+::
+
+        0  0  1  1    operand1
+        0  1  0  1    operand2
+        ----------
+        0  1  1  1    (operand1 | operand2) - returned result
+
+
+
+Here is an example of the bitwise OR used in a snippet of C++
+code:
+
+
+
+::
+
+        int a =  92;    // in binary: 0000000001011100
+        int b = 101;    // in binary: 0000000001100101
+        int c = a | b;  // result:    0000000001111101, or 125 in decimal.
+
+
+
+Example Program
+---------------
+
+A common job for the bitwise AND and OR operators is what
+programmers call Read-Modify-Write on a port. On microcontrollers,
+a port is an 8 bit number that represents something about the
+condition of the pins. Writing to a port controls all of the pins
+at once.
+
+
+
+PORTD is a built-in constant that refers to the output states of
+digital pins 0,1,2,3,4,5,6,7. If there is 1 in an bit position,
+then that pin is HIGH. (The pins already need to be set to outputs
+with the pinMode() command.) So if we write ``PORTD = B00110001;``
+we have made pins 2,3 & 7 HIGH. One slight hitch here is that we
+*may* also have changeed the state of Pins 0 & 1, which are used by
+the Arduino for serial communications so we may have interfered
+with serial communication.
+
+
+
+::
+
+         Our algorithm for the program is:
+
+
+-  Get PORTD and clear out only the bits corresponding to the pins
+   we wish to control (with bitwise AND).
+-  Combine the modified PORTD value with the new value for the pins
+   under control (with biwise OR).
+
+
+
+::
+
+    int i;     // counter variable
+    int j;
+    
+    void setup(){
+    DDRD = DDRD | B11111100; // set direction bits for pins 2 to 7, leave 0 and 1 untouched (xx | 00 == xx)
+    // same as pinMode(pin, OUTPUT) for pins 2 to 7
+    Serial.begin(9600);
+    }
+    
+    void loop(){
+    for (i=0; i<64; i++){
+    
+    PORTD = PORTD & B00000011;  // clear out bits 2 - 7, leave pins 0 and 1 untouched (xx & 11 == xx)
+    j = (i << 2);               // shift variable up to pins 2 - 7 - to avoid pins 0 and 1
+    PORTD = PORTD | j;          // combine the port information with the new information for LED pins
+    Serial.println(PORTD, BIN); // debug to show masking
+    delay(100);
+       }
+    }
+
+
+
+Bitwise XOR (^)
+---------------
+
+There is a somewhat unusual operator in C++ called bitwise
+EXCLUSIVE OR, also known as bitwise XOR. (In English this is
+usually pronounced "eks-or".) The bitwise XOR operator is written
+using the caret symbol ^. This operator is very similar to the
+bitwise OR operator \|, only it evaluates to 0 for a given bit
+position when both of the input bits for that position are 1:
+
+
+
+::
+
+        0  0  1  1    operand1
+        0  1  0  1    operand2
+        ----------
+        0  1  1  0    (operand1 ^ operand2) - returned result
+
+
+
+Another way to look at bitwise XOR is that each bit in the result
+is a 1 if the input bits are different, or 0 if they are the same.
+
+
+
+Here is a simple code example:
+
+
+
+::
+
+        int x = 12;     // binary: 1100
+        int y = 10;     // binary: 1010
+        int z = x ^ y;  // binary: 0110, or decimal 6
+
+
+
+The ^ operator is often used to toggle (i.e. change from 0 to 1, or
+1 to 0) some of the bits in an integer expression. In a bitwise OR
+operation if there is a 1 in the mask bit, that bit is inverted; if
+there is a 0, the bit is not inverted and stays the same. Below is
+a program to blink digital pin 5.
+
+
+
+::
+
+    // Blink_Pin_5
+    // demo for Exclusive OR
+    void setup(){
+    DDRD = DDRD | B00100000; // set digital pin five as OUTPUT 
+    Serial.begin(9600);
+    }
+    
+    void loop(){
+    PORTD = PORTD ^ B00100000;  // invert bit 5 (digital pin 5), leave others untouched
+    delay(100);
+    }
+
+
+
+See Also
+
+
+-  `&& <http://arduino.cc/en/Reference/Boolean>`_ (Boolean AND)
+-  `\|\| <http://arduino.cc/en/Reference/Boolean>`_ (Boolean OR)
+