Engineering 1040: Mechanisms & Electric Circuits Fall 2011

Engineering 1040: Mechanisms & Electric Circuits Fall 2011 Introduction to C Programming

Basic Rules When Programming in C Language • At the end of each line with instructions a semi-colon (;) has to be placed. Eg: a=a+3; • There are two methods of indicating comments. • For single lines: //comment. • For multiple lines: /* This is comment 1; This is comment 2; */. • Functions, statements, etc., should be between { }. Eg: void main(void) //Function { //Add code }

The Structure of a C Program //Header files #include <18f4550.h> //Declaring variables int a, b, c, par1, d; charzz, s3, temp; //Making prototypes int calc (intp); //Function int calc (intp) { p=p+1; //Add code return p; } //Main function void main(void) { //Add code a=calc(3); } • Header files. • Declaration of global variables. • Declaration of Function Prototypes. • Function Declaration. • Main function. Main function is the most important part of the C program. Most of the time we make modifications in main function

Header files • Header files include the standard functions that will used elsewhere in the program. • Text from the specified file is used at this point of the compilation. • These will call the library functions. #include < 18f4550.h > - Functions specific to the PIC #include < adc.h > - A/D converter functions. #include < xlcd.h > - Functions used for display by a LCD screen. #include < delays.h > - Delay functions in the program. #include < stdio.h > - Standard input and output functions. • All header files used in standard C programming is valid in microcontroller programming .

Variable types (1)

Variable types (2) • Possible ways to give variable a the decimal value 15: a = 15; //Decimal a = 0b0000 1111; //Binairy a = 0x0F; //Hexadecimal

Operators (1) • Relational operators • Bit operators

Operators (2) • Mathematical operators • Increasing and decreasing: x--; //This is the same as x = x – 1; x++; //This is the same as x = x + 1; • Example: int a, b, c; a = 19; //a 00010011 b = 6; //b 00001110 c = a & b; //c 00000010 -> 2

Statements (1) • IF...ELSE if (a==0) //If a is similar to 0... { b++; //...than increase b by 1 } else //otherwise { b--; //decrease b by 1 } • WHILE while (a>3) //As long as a is higher than 3 { b = b + 3; //Add 3 to b a--; //Decrease a by 1 }

Statements (2) • FOR for (i = 0 ; i < 100 ; i++) //From i=0 to i=100 with step size 1 { b++; //Increase b by 1 a--; //Decrease a by 1 }

Bootloader • When a bootloader is used, a special part of code has to be included in the program, after the #include statements. //Always use this code when using with a boot oader #pragma code _RESET_INTERRUPT_VECTOR = 0x000800 void _reset (void) { _asmgoto _startup _endasm } #pragma code #pragma code _HIGH_INTERRUPT_VECTOR = 0x000808 void _high_ISR (void) { ; } #pragma code #pragma code _LOW_INTERRUPT_VECTOR = 0x000818 void _low_ISR (void) { ; } #pragma code //End bootloader code

Programming Pins & Ports (1) • If PORTB is used for writing to and reading from pins on port B. • Writing a, • ‘1’ to one of the bits of PORTB results in a high voltage on the output pin. • ‘ 0’ will result in a low voltage. • The MSB (most significant bit, the most left one) is used for pin B7, the LSB for pin B0.

Programming Pins & Ports (2) • Declaring all the pins of a port: • Declaring a specific pin of a port to high or low:

Programming Pins & Ports (3) • Instead of using PORT the command LAT could also be used in declaring pins. Example: • LATD = 0x00; // Set all port D to low • LATCbits.LATC0 = 0; //Set pin C0 to low • LATCbits.LATC1 = 1; //Set pin C1 to high

Programming Pins & Ports (4) • Declaring a port as an output port: • Use ‘1’ for Input • Use ‘0’ for Output Example: • TRISD = 0b11111111; //Set all pins in port D as inputs • TRISD = 0b00000000; //Set all pins in port D as outputs • TRISD = 0b10101010; //Set pins 0,2,4,6 of port D as outputs //Set pins 1,3,5,7 of port D as inputs

Coding the Wall-Following Mobile Robot Platform • goForward(void) –go forward by 1 step. • turnRight(int stepNum) – turn to the right side by the angle specified by the integer stepNum • readFrontSensor(void) – read the value of the front sensor Homework: • Using the above given functions write a code in C language, • Write a function for the robot to turn left (call this function turnLeft(int stepNum) ) • Write a function for reading the left sensor (call this function readLeftSensor (int stepNum) ) • Write a function for the robot to move forward a number of steps given by x (call this function goForwardx( (int x) )

void turnRight(int stepNum) { int i = 0; while(I < stepNum) { rotateCW(2); // Rotate motor two by one step rotateCW(1); // Rotate motor by one step Delay1KTCYx(50); // Changing the argument in the delay function will change the speed at which // the motor rotates. Delay equals 1000 x 50 x 1/12 = 4.167 ms i++; LATD = 0x00; // Set all port D to 0 } return; }

void goForward(void){ rotateCCW(2); // Rotate motor two step rotateCW(1); // Rotate motor one step Delay1KTCYx(50); // Changing the argument in the delay function will change the // speed at which the motor rotates. Delay equals 1000 x 50 x // 1/12 = 4.167 ms LATD = 0x00; // Set all port D to 0 }

Wall Follow Algorithm (1) Write a pseudo code for the “wallee” robot to follow a wall on the left hand side using the left sensor. If (leftsensor > sensorreading_close) { rightturn(10); goforwardx(5); } If (leftsensor < sensorreading_far) { leftturn(10); goforwardx(5); } else (leftsensor <= sensorreading_close) && (l sensorreading_far > =200) { goforwardx(10); } Left Sensor Wall Sensorreading_close Sensorreading_far

Wall Follow Algorithm (2) • Write a pseudo code for the “wallee” robot to follow a wall on the left hand side using the left sensor. If (leftsensor > 400) { rightturn(10); goforwardx(5); } If (leftsensor < 200) { leftturn(10); goforwardx(5); } else (leftsensor <= 400) && (leftsensor > =200) { goforwardx(10); } Left Sensor Wall

Engineering 1040: Mechanisms & Electric Circuits Fall 2011