C Programming Language

Size: px

Start display at page:

Download "C Programming Language"

Kenneth Horn
5 years ago
Views:

2 C Programming Language Advantages over assembly language for microcontrollers: More portable Math functions Readability Maintainability

3 Editing C End-of-line ignored Use line breaks/tabs/indent for readability Lines end in semicolon ; Use Braces {} to group things Comments: your code must have comments! Standard C comment between /* and */ (no nesting) C++ style common too, between // and end of line

4 Pre-Processor Performs text replacement before compile Commands marked with # the pound #include inserts entire file #include <stdio.h> // compiler library #include yourfile.h //paste your file right here.h files are header files Common declarations Port, register names defined for chip (PORTB) #define does search and replace #define this that // replace every this with that #define MAX 100 // common for defining constants

5 Variables Names for memory locations int: 16 bit float: floating point (3.14) char: 8 bit unsigned char: signed char: -128 to 127 long int or long: 32 bit

6 mikroc variable types

7 Logical Operators x =10 x > 8 // returns 1 x ==10 // returns 1 x < 100 // returns 1 x > 20 // returns 0 x!= 10 // returns 0 x >= 10 // returns 1 x <=10 // returns 1

8 Logical Operators x = 7; x > 0 && x < 10 // returns 1 x > 0 x < 10 // returns 1 x >=0 && x <=10 // returns 1 x >=0 && x < 5 // returns 0 a = 10; b = 20; c = 30; d = 40; a > b && c > d // returns 0 b > a && d > c // returns 1 a > b d > c // returns 1

Bitwise Operators 0xFA & 0xEE returns 0xEA 0xFA: 1111 1010 0xEE: 1110 1110 0xEA: 1110 1010 0x01 0xFE returns 0xFF 0x08: 0000 0001 0xFE: 1111 1110 0xFE: 1111 1111 0x14 >> 2 returns 0x05 (shift

9 Bitwise Operators 0xFA & 0xEE returns 0xEA 0xFA: xEE: xEA: x01 0xFE returns 0xFF 0x08: xFE: xFE: x14 >> 2 returns 0x05 (shift 0x14 right by 2 digits) 0x14: >>2: xAA 0x1F returns 0xB5 0xAA: x1F: xB5: xAA returns 0x55 0xAA: x55: 0x55: x05:

10 Data Accessing /* Input/Output Ports initialization */ // Port A initialization Accessing Registers TRISA=0x01; // Initialize direction TRISB=0b ; PORTA=0x00; // Initialize state Accessing Individual Bits INTCON.GIE = 0; // Clear Global Interrupt Bit (GIE) //GIE is defined in the definition file INTCON.B0 = 0; // Clear bit 0 in INTCON register INTCON.F5 = 1; // Set bit 0 in INTCON register

11 Accessing Individual Bits You can declare a sbit variable in a unit in such way that it points to a specific bit in SFR register: sbit Abit at PORTB.B0; // this is where Abit is fully defined void main(){ Abit=1; } The mikroc compiler provides a bit data type that may be used for variable declarations. It can not be used for argument lists, and function-return values bit bf; // bit variable

12 Arrays unsigned int Total[5]; Total[1] = 25; unsigned char months[ ] ={31,28,31,30,31,30,31,31,30,31,30,31}; unsigned char Hex_Letters[ ] = { A, B, C, D, E, F }; unsigned char Mystring[ ]= COMP ; unsigned char Mystring[ ] = { C, O, M, P, \0 }; unsigned char Q[2][2] = { {1,0}, {0,1} };

13 Variable declarations Local variables Declared inside a function Names can be reused Not shared with other functions Global variables Declared outside functions All functions can see and use them Programming style determines use

14 Math Operators Main reason to use C over assembly Standard arithmetic: + - * / Modulus % gives remainder: 7 % 2 = 1 ++ and -- increment and decrement x++; // same as x = x + 1 += is a shortcut (-=, *=, /= etc work too) x+=2; // same as x = x + 2

15 Branches and Loops if (x > y) { x = 1; // if true } else { x = 34; // if false } for (count=0; count<7; count++) { // count is 0 through 6 x = x + count; // calculated 7 times } Mechatronics Engr 415 Spring 2007

16 Branches and Loops continued while (x > y) { x = 1; // infinite loop? } switch (numx) { case 1: // this happens if x = 1 y = y+x; break; case 3: // if x is 3 this executes y = 23; break; default: // otherwise this happens y = 0; break; } Mechatronics Engr 415 Sprig 2007

17 Pointers and Arrays Pointers: variable location rather than value Not used much in small microcontrollers int x; // regular int int *p; // pointer to int p = &x; // p has address of x x = *p; // x has value pointed to by p Arrays: vector of variables, index in [] int i, pwm_out[8]; // 8 ints for (i=0;i<8;i++) { } pwm_out[i]=0; // clear array Mechatronics Engr 415 Spring 2007

18 Functions: Return a number or VOID #include <math.h> // need sin float sx, x; // declare variables (global) int z, z2; // Function square starts here int square(int x) // custom user-written function to do square of 2 numbers { int y; // local variable y = x*x; // function calculation return y; // send this back } // Function main starts here void main(void) // there is always a main function { } x =1.57; // radians sx = sin(x); // function call z = 2; // units? z2 = square(z); // function call

19 Write assembly in C code asm { Assembly language instructions... }

C Programming Language. Microcomputer Architecture and Interfacing Colorado School of Mines Professor William Hoff

C Programming Language. Microcomputer Architecture and Interfacing Colorado School of Mines Professor William Hoff C Programming Language 1 C C is better to use than assembly for embedded systems programming. You can program at a higher level of logic than in assembly, so programs are shorter and easier to understand.