embedded c operators

8/13/2019 Embedded C Operators

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Agenda

Evaluate and explain the results of operatorsused in C

I/O operations

Arithmetic Bitwise

Logical

Relational

Pre- and post- increment and decrement

Explain the precedence of the operators

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I/O Operations

Embedded microcontrollers must interactdirectly with outside hardware

Through parallel ports on the controller

Microcontroller header files use sfrb and sfrw toassign labels to parallel ports Special Function Register (Byte or Word)

Defines labels such as DDRB, PINA, PORTB, etc

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I/O Operations

To define inputs/outputs write to DDRx Data direction register (could be A, B, C, etc)

DDRx = 0xff; //make all lines outputs

DDRx = 0; // make all lines inputs

To write to an output port PORTC = value;

To read an input port

Variable_name = PINA;

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I/O Operations

Example:

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#include //register definition fileunsigned char z; //z is an 8-bit number void main (void) {

DDRA = 0; //make Port A all inputsDDRB = 0xff; //make Port B all outputswhile (1) {

z = PINA; //read Port APORTB = z + 1; //write the value (+1) to Port B

}}


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I/O Operations Hands-on: write a C program to initialize Port C as all outputs and

Port B as all inputs. Read Port B, negate the number read and thenoutput the new number on Port C. Assume you are to use an

Atmega128.

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I/O Operations Hands-on: write a C program to initialize Port C as all outputs and

Port B as all inputs. Read Port B, negate the number read and thenoutput the new number on Port C. Assume you are to use an

Atmega128.

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#include //register definition fileunsigned char x; //x is an 8-bit number void main (void) {

DDRB = 0; //make Port B all inputsDDRC = 0xff; //make Port C all outputswhile (1) {

x = PINB; //read Port BPORTC = -x; //write the value to Port C

}}


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Arithmetic Operators The arithmetic operators in C are:

Multiply: *

Divide: /

Addition: +

Subtraction: -

Negate: -

Modulo: %

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Multiply: *

Divide: /

Addition: +

Subtraction: -

Negate: -

Modulo: %

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Evaluate:

char x = 10, y = 3, z;z = x % y;


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Multiply: *

Divide: /

Addition: +

Subtraction: -

Negate: -

Modulo: %

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The modulo operator returns the

remainder of x/y

Evaluate:

char x = 10, y = 3, z;z = x % y;

z =1


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Multiply: *

Divide: /

Addition: +

Subtraction: -

Negate: -

Modulo: %

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Evaluate:

char x = 15, y = 4, z;z = x / y;


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Multiply: *

Divide: /

Addition: +

Subtraction: -

Negate: -

Modulo: %

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Evaluate:

char x = 15, y = 4, z;z = x / y;

z = 3

x, y, and z are all 8 bit integers


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Bitwise Operators The bitwise operators in C are:

Ones compliment ~

Left shift >

AND &

OR |

Exclusive OR ^

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Ones compliment ~

Left shift >

AND &

OR |

Exclusive OR ^

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Evaluate:

char x = 4, y = 1, z;z = x


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Ones compliment ~

Left shift >

AND &

OR |

Exclusive OR ^

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Evaluate:

char x = 4, y = 1, z;z = x


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Ones compliment ~

Left shift >

AND &

OR |

Exclusive OR ^

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Evaluate:

char x = 4, y = 1, z;z = x | y;


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Ones compliment ~

Left shift >

AND &

OR |

Exclusive OR ^

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Evaluate:

char x = 4, y = 1, z;z = x | y;

z = 5

x (in binary) is 0b00000100

y (in binary) is 0b00000001When ORed together : 0b00000101


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Logical Operators The logical operators in C are:

AND &&

OR ||

Results in TRUE or FALSE TRUE is any non-zero result

FALSE is a result equal to 0

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Evaluate:

char x = 5, y = 2, z;z = x && y;


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Logical Operators The logical operators in C are:

AND &&

OR ||

Results in TRUE or FALSE TRUE is any non-zero result

FALSE is a result equal to 0

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Evaluate:

char x = 5, y = 2, z;z = x && y;

TRUE because both operands are non-zero (i.e.; TRUE && TRUE = TRUE)


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Relational Operators The relational operators in C are:

Is equal to ==

Is not equal to !=

Less than =

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Is equal to ==

Is not equal to !=

Less than =

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Evaluate:

char x = 5, y = 2, z;if (x = y) then z = 1 else z = 0;


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Is equal to ==

Is not equal to !=

Less than =

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Evaluate:

char x = 5, y = 2, z;if (x = y) then z = 1 else z = 0;

z =1

This is a common error in C (and otherlanguages). There is only one = between x

and y, so this is actually an assignment inwhich we assign the value of y to x. Cevaluates an assignment as TRUE, so z = 1.BTW: x = 2 and y =2


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Increment and Decrement Operators The increment operator in C is:

++

++x pre-increment

x++ post-increment

The decrement operator in C is: --

--x pre-decrement

x-- post-decrement

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Evaluate:

char x = 5, y = 1, z;z = x * y++;


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++

++x pre-increment

x++ post-increment


--x pre-decrement

x-- post-decrement

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Evaluate:

char x = 5, y = 1, z;z = x * y++;

z =5 and y = 2

This is a post-increment, so x (5) ismultiplied by y (1), and then y is

incremented to 2


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++

++x pre-increment

x++ post-increment


--x pre-decrement

x-- post-decrement

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Evaluate:

char x = 5, y = 1, z;z = x * ++y;


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++

++x pre-increment

x++ post-increment


--x pre-decrement

x-- post-decrement

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Evaluate:

char x = 5, y = 1, z;z = x * ++y;

z = 10 and y = 2

In this case y is incremented before themultiplication (pre-increment)


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Compound Assignment Operators A short hand version of other C statements:

A += 3; same as A = A + 3;

B -= 2; same as B = B- 2;

C |= 3; same as C = C | 3;

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Write the short hand versions of:

C = C * 5;D = D /2;E = E & 3;F = F ^ 5;


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Compound Assignment Operators A short hand version of other C statements:

A += 3; same as A = A + 3;

B -= 2; same as B = B- 2;

C |= 3; same as C = C | 3;

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Write the short hand versions of:

C = C * 5; C *= 5;D = D /2; D /= 2;E = E & 3; E &= 3;F = F 5; F =5;


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Summary

Evaluated and explained the results ofoperators used in C

I/O operations (using the port names)

Arithmetic (*, /, +, -, and %) Bitwise (&, , ~, ^, and |)

Logical (&& and ||)

Relational (==, !=, , =)

Pre- and post- increment and decrement (++ and --)

Explained the precedence of the operators

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embedded c operators

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