1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
|
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html>
<head>
<title>Arduino - BitwiseAnd </title>
<link rel='stylesheet' href='arduino.css' type='text/css' />
<meta name="verify-v1" content="TtxFIEJAB6zdJ509wLxjnapQzKAMNm9u0Wj4ho6wxIY=" />
</head>
<body>
<div id="page">
<!--PageHeaderFmt-->
<div id="pageheader">
<div class="title"><a href="http://www.arduino.cc"/>Arduino</a></div>
<div class="search">
<!-- SiteSearch Google -->
<FORM method=GET action="http://www.google.com/search">
<input type=hidden name=ie value=UTF-8>
<input type=hidden name=oe value=UTF-8>
<INPUT TYPE=text name=q size=25 maxlength=255 value="">
<INPUT type=submit name=btnG VALUE="search">
<input type=hidden name=domains value="http://www.arduino.cc/">
<input type=hidden name=sitesearch value="http://www.arduino.cc/">
</FORM>
<!-- SiteSearch Google -->
</div>
</div>
<!--/PageHeaderFmt-->
<!--PageLeftFmt-->
<div id="pagenav" style="text-align: right">
<div style="float: left;">
<p><a class='wikilink' href='http://arduino.cc/en/Main/Buy'>Buy</a>
|
<a class='wikilink' href='http://arduino.cc/en/Main/Software'>Download</a>
|
<a class='wikilink' href='Guide_index.html'>Getting Started</a>
|
<a class='wikilink' href='http://arduino.cc/en/Tutorial/HomePage'>Learning</a>
|
<a class='wikilink' href='index.html'>Reference</a>
|
<a class='wikilink' href='http://arduino.cc/en/Main/Hardware'>Hardware</a>
|
<a class='wikilink' href='FAQ.html'>FAQ</a>
</p>
<p class='vspace'></p>
</div>
<a class="urllink" href="http://www.arduino.cc/blog/" rel="nofollow">Blog »</a> |
<a class="urllink" href="http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl" rel="nofollow">Forum »</a> |
<a class="urllink" href="http://www.arduino.cc/playground/" rel="nofollow">Playground »</a>
</div>
<!--/PageLeftFmt-->
<div id="pagetext">
<!--PageText-->
<div id='wikitext'>
<p><strong>Reference</strong> <a class='wikilink' href='index.html'>Language</a> (<a class='wikilink' href='Extended.html'>extended</a>) | <a class='wikilink' href='Libraries.html'>Libraries</a> | <a class='wikilink' href='Comparison.html'>Comparison</a> | <a class='wikilink' href='Changes.html'>Changes</a>
</p>
<p class='vspace'></p><h2>Bitwise AND (&), Bitwise OR (|), Bitwise XOR (^)</h2>
<h4>Bitwise AND (&)</h4>
<p>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 <a class='urllink' href='http://www.arduino.cc/playground/Code/BitMath' rel='nofollow'>here.</a>
</p>
<p class='vspace'></p><h4>Description and Syntax</h4>
<p>Below are descriptions and syntax for all of the operators. Further details may be found in the referenced tutorial.
</p>
<p class='vspace'></p><h4>Bitwise AND (&)</h4>
<p>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:
</p>
<p class='vspace'></p><pre> 0 0 1 1 operand1
0 1 0 1 operand2
----------
0 0 0 1 (operand1 & operand2) - returned result
</pre>
<p class='vspace'></p><p>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:
</p>
<p class='vspace'></p><pre> int a = 92; // in binary: 0000000001011100
int b = 101; // in binary: 0000000001100101
int c = a & b; // result: 0000000001000100, or 68 in decimal.
</pre>
<p class='vspace'></p><p>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.
</p>
<p class='vspace'></p><p>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
</p>
<p class='vspace'></p><h4>Bitwise OR (|)</h4>
<p>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:
</p>
<p class='vspace'></p><pre> 0 0 1 1 operand1
0 1 0 1 operand2
----------
0 1 1 1 (operand1 | operand2) - returned result
</pre>
<p class='vspace'></p><p>Here is an example of the bitwise OR used in a snippet of C++ code:
</p>
<p class='vspace'></p><pre> int a = 92; // in binary: 0000000001011100
int b = 101; // in binary: 0000000001100101
int c = a | b; // result: 0000000001111101, or 125 in decimal.
</pre>
<p class='vspace'></p><h4>Example Program</h4>
<p>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.
</p>
<p class='vspace'></p><p>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 <code>PORTD = B00110001;</code> we have made pins 2,3 & 7 HIGH.
One slight hitch here is that we <em>may</em> 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.
</p>
<p class='vspace'></p><pre> Our algorithm for the program is:
</pre><ul><li>Get PORTD and clear out only the bits corresponding to the pins we wish to control (with bitwise AND).
</li><li>Combine the modified PORTD value with the new value for the pins under control (with biwise OR).
</li></ul><p class='vspace'></p><pre>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);
}
}
</pre>
<p class='vspace'></p><h4>Bitwise XOR (^)</h4>
<p>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:
</p>
<p class='vspace'></p><pre> 0 0 1 1 operand1
0 1 0 1 operand2
----------
0 1 1 0 (operand1 ^ operand2) - returned result
</pre>
<p class='vspace'></p><p>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.
</p>
<p class='vspace'></p><p>Here is a simple code example:
</p>
<p class='vspace'></p><pre> int x = 12; // binary: 1100
int y = 10; // binary: 1010
int z = x ^ y; // binary: 0110, or decimal 6
</pre>
<p class='vspace'></p><p>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.
</p>
<p class='vspace'></p><pre>
// 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);
}
</pre>
<p class='vspace'></p><p>See Also
</p><ul><li><a class='wikilink' href='Boolean.html'>&&</a>(Boolean AND)
</li><li><a class='wikilink' href='Boolean.html'>||</a>(Boolean OR)
</li></ul><p class='vspace'></p><p><a class='wikilink' href='index.html'>Reference Home</a>
</p>
<p class='vspace'></p><p><em>Corrections, suggestions, and new documentation should be posted to the <a class='urllink' href='http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?board=swbugs' rel='nofollow'>Forum</a>.</em>
</p>
<p class='vspace'></p><p>The text of the Arduino reference is licensed under a
<a class='urllink' href='http://creativecommons.org/licenses/by-sa/3.0/' rel='nofollow'>Creative Commons Attribution-ShareAlike 3.0 License</a>. Code samples in the reference are released into the public domain.
</p>
</div>
</div>
<!--PageFooterFmt-->
<div id="pagefooter">
<a href='#'>Edit Page</a> | <a href='#'>Page History</a> | <a href='#' target='_blank'>Printable View</a> | <a href='http://arduino.cc/en/Site/AllRecentChanges'>All Recent Site Changes</a>
</div>
<!--/PageFooterFmt-->
</div>
</body>
</html>
|
