Embedded system (Chapter )

PIC PROGRAMMING
IN C
DEPARTMENT OF ELECTRICAL ENGINEERING
POLITEKNIK SULTAN HAJI AHMAD SHAH
CHAPTER 5 – Part 1
EC501 EMBEDDED SYSTEM APPLICATIONS

Outcomes of today’s class
 Student should be able to:
1. Identify C programming languages for
PIC18
2. Explain the structure of C program for
PIC18
3. Discuss C Data type widely use by PIC

Review
• Microcontroller process input data base on a
program (hex file) stored in microcontroller.
• Compilers produce hex files that we download
into the ROM of the microcontroller.
• In this chapter we will learn C programming
language to write program for PIC18F4550.
Input
signal
Microcontroller
(Process)
Output
signal

Why Program the PIC18 in C?
Reasons For Writing Programs In C Instead Of Assembly:
1. It is easier and less time consuming.
2. C is easier to modify and update.
3. You can use code available in function libraries.
4. C code is portable to other microcontrollers with
little or no modification.

Standard Method
 There is no 100% correct ways to write C program,
anyway there are guide lines to follow.

Standard Method
a. C Comments
2 ways to write comment:
i. Comment for multiple line:
/* Chapter 5
Title: C programming for PIC18F4550 */
ii. Comment for one line only:
// wait until SW1 press

b. Include Header File
• It enables the compiler to include file which
define standard keyword for PIC based on
model.
• Eg.:
Standard Method

c. Configuration Bits
• A macro that writes a value into the special register that
controls the core executing operations of the
microcontroller.
• Configuration bit can be set in development software
(eg.: MPLAB IDE).
• If the configuration bits are not specified correctly, the
PIC MCUs might not run the application code properly
Standard Method

Configuration Bits
 Eg.:
 1. Confuguration bit for PIC16F877A
__CONFIG 0Xf32
 2. Configuration bit for PIC18F4550

 d. Include Libraries, Functions declaration and
Global variables
 Placed:
- include other header file,
- libraries,
- to declare functions prototype
- global variables.
 This section can be leaved blank depend on
program writer.
Standard Method

 e. Function Name
 It is the basic building block in C programming.
 C program must have at least the function
main( ).
 Eg.: void main (void)
 The void means the main( ) function doesn't
return any value when it exit (finish running).
Standard Method

 f. Function Body
 Every function, including main( ), must have a
body enclosed in braces { }.
 The curly braces are to signify the block of
codes belonging to main( ).
 Do take note that there MUST NOT be a
semicolon after the closing brace.
Basic rules for programming in C

Exercise
 Identify the following from the program above :
1. Comment
2. Include header file
3. Configuration bit
4. Function
5. Function body
Tem_str

#include<xc.h>
//Configuration bits for PIC18f4550
#pragma config PLLDIV = 5 //20MHz devide by 5 to obtain 4MHz to enter PLL and become 96MHz
#pragma config CPUDIV = OSC1_PLL2 //Primary Oscillator source is 96MHz/2
#pragma config USBDIV = 2 //USB peripheral clock source from 96MHz/2
#pragma config FCMEN = ON //Fail-Safe Clock Monitor Enable bit
#pragma config IESO = ON //Internal/External
#pragma config PWRT = ON //Power Up Timer Enable bit
#pragma config BOR = OFF //Brown-out Reset Enable bit
#pragma config WDT = OFF //Watch-dog Timer Enable bit
#pragma config VREGEN = ON //Enable USB Voltage Regulator
#pragma config CCP2MX = ON //CCP2 at RC1
#pragma config PBADEN = ON //PORTB analog pin as analog input after Reset
#pragma config LPT1OSC = OFF //Timer 1 configured for high power operation
#pragma config MCLRE = ON //PCLR pin enable, RE3 input disable
#pragma config STVREN = ON //Stack overflow will cause Reset
#pragma config LVP = OFF //Low voltage programming disable
#pragma config XINST = OFF //Instruction set extension and Indexed Addressingmode enabled
#pragma config DEBUG = OFF //Debug disable, RB6 and RB7 as normal IO
#pragma config WRTB = ON //Boot Block Write Protect enable
void main(void)
{
TRISA2=0; //make pin RA2 as output (LED)
LATA2=0; //LED on RA2 "OFF"
while(1);
}

Radix Format
 Radix format is the way a value is being presented in
C language
 There are four methods to present value:
Radix Format
Binary 0bnumber or 0Bnumber
Octal Onumber or number
Decimal number
Hexadecimal 0xnumber or 0Xnumber

Radix Format - example
1. Write a statement to sent binary value 00001111 to Port A.
Solution:
PORTA= 0b00001111;
2. Convert the value in Question 1 into the following radix
format:
a) Decimal
b) Hexadecimal
Solution:
a) PORTA=15;
b) PORTA=0x0F;

Data Type
 Data Type is type assigned to variable to determine
the size and how the variable being interpreted.
 Fundamental Type

 Modified Integer Types.
 Qualifiers: unsigned, signed, short and long
Data Type

 Modified Floating Point Types
Data Type

– The unsigned char is an 8-bit data type that takes value
in range of 0-255 (00-FFH)
– C compilers use the signed char as the default unless we
put the keyword unsigned in front of the char.
– Example 5.1:
• Write a C program to send value 0-255 to Port B
Solution:
#include <P18F4550.h>
void main(void)
{
unsigned char z;
TRISB=0;
for(z=0;z<=255;z++)
PORTB=z;
while(1);
}
Unsigned Char

Data Type - Unsigned Char
• Example 5.2
Write a C program to send hex values 8D to Port B.
Solution:
unsigned char z=0x8D;
void main(void)
{
TRISB=0;
PORTB=z;
while(1);
}

• The signed char is an 8-bit data type that
uses the most significant bit (D7 of D7-D0) to
represent the – or + value.
• As a result, we have only 7 bits for the
magnitude of the signed number, giving us
value from -128 to +127.
D7 D6 D5 D4 D3 D2 D1 D0
Sign
bit magnitude
Signed Char

Data Type - Signed Char
• Example 5-4
Write a C18 program to send values of -4 to
+4 to Port B.
Solution:
void main(void)
{
char mynum[ ]={+1,-1,+2,-2,+3,-3,+4,-4};
signed char z;
TRISB=0; //make Port B an output
for (z=0;z<8;z++)
{
PORTB=mynum[z];
}
while(1); //stay here forever

• The unsigned int is a 16-bit data type that takes a value
in the range of 0 to 65,535 (0000 – FFFFH).
• It also used to set counter value of more than 256.
• Example:
unsigned int i;
Data Type - Unsigned Int

• Example 5-5
Write a C18 program to toggle all bits of Port
B 50,000 times.
Solution:
void main(void)
{
unsigned int z;
for (z=0;z<=50000;z++)
{
PORTB=0x55;
PORTB=0xAA;
}
}

• Signed int is a 16-bit data type that uses the most
significant bit (D15 of D15-D0) to represent the – or +
value. As a result, we have only 15bits for the magnitude
of the number, or value from -32,768 to + 32,767.
• Example:
signed int i;
Or
int i;
Signed Int

Other Data Types
• The unsigned int is limited to value 0-65,535
(0000 – FFFFH).
• The C18 C compiler supports both short long
and long data types, if we want values greater
than 16-bit.
• See Table 5.1. The short long value is 24 bits
wide, while the long value is 32 bits wide.

EXERCISE
Write a C18 program to toggle all bits of Port B
100,000 times.
Solution:
void main(void)
{
unsigned short long z;
for (z=0;z<=100000;z++)
{
PORTB=0x55;
PORTB=0xAA;
}
}

Review question
1. Give the reason why you choose C programming
instead of assembly?
2. Give the magnitude of unsigned char and signed
char data types.
3. If we declaring a variable for person’s age, we
should use the ___data type.

Conclusion – outcomes of the day
Students should be able to:
1. Identify C programming languages for PIC18
2. Explain the structure of C program for PIC18
3. Discuss C Data type widely use by PIC
Have you achieved the outcomes?

Embedded system (Chapter )

More Related Content

What's hot (20)

Viewers also liked (17)

Similar to Embedded system (Chapter ) (20)

Embedded system (Chapter )