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diff --git a/source/arduino/bitwiseand.rst b/source/arduino/bitwiseand.rst deleted file mode 100644 index 8d4eb3f..0000000 --- a/source/arduino/bitwiseand.rst +++ /dev/null @@ -1,230 +0,0 @@ -.. _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) - |