Bài giảng Microprocessing Systems - Chapter 8: C Programming for 8051

ĐH Bách Khoa TP.HCM

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The 8051 Microcontroller

Chapter 8

C Programming for 8051

TS. Lê Chí Thông

chithong@hcmut.edu.vn

sites.google.com/site/chithong

Ho Chi Minh City University of Technology

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Outline

• Structure of a C program

• Using Keil

• Declaration of the types of memory

• Variable types

• Keywords in Keil C51

• Functions

• Operations – Statements

• Time delay

• I/O programming

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References

• Cx51 Compiler User Guide (pdf)

http://www.neuromorphs.net\nm\raw-attachment\wiki\2010\usb10\C51.PDF

• Matthew Kramer, Writing C Code for the 8051 (pdf)

http://www.kel.ftn.uns.ac.rs/predmeti/3/mpe/razno/writing_c_code_8051.pdf

• M. Mazidi, J. Mazidi, and R. McKinlay, The 8051 Microcontroller

and Embedded Systems Using Assembly and C (2^nded.)

• Chung-Ping Young, 8051 Programming in C (pdf)

• Ibrahim Kamal, C programming for 8051 using KEIL IDE,

http://www.ikalogic.com/part-2-c-programming-for-8051-using-

keil-ide/

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Blinky Program

(Schematic)

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Blinky Program

void Delayms (unsigned int ms) {

//Documentatons

unsigned int i;

while (ms) {

i = 115;

/**************************

Blinky program

Date: 05-Apr-2012

while (i> 0) i--;

ms--;

Version: 1.0

***************************/

//Preprocessor Statements

#include <reg51.h>

}

// Main Program

main (void) {

while (1) {

#define ON 1

#define OFF 0

// Global declarations

sbit LED1=P1^0;

LED1 = ON; // Turn on LED1

Delayms (500); // Delay 500 ms

LED1 = OFF; // Turn off LED1

Delayms (500); // Delay 500 ms

}

// Subprograms

/* Delay in milliseconds for a 11.0592 MHz crystal */

source

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From the C program

to the machine language

Source: http://www.ikalogic.com/part-2-c-programming-for-8051-using-keil-ide/

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C Programming for the 8051

• C programming is less time consuming, but has

larger hex file size

• The reasons for writing programs in C

– It is easier and less time consuming to write in C than

Assembly

– C is easier to modify and update

– You can use code available in function libraries

– C code is portable to other microcontroller with little

of no modification

Source: Chung-Ping Young, 8051 Programming in C

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Structure of a C program

Documentations

Preprocessor Statements

Global Declarations

Subprograms (User defined functions)

Main Program (Main function)

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Structure of a C program

//Subprograms

//Documentatons

//Name of the program, programmer,

//and other details

Void function1 (int x) {

//Statements

}

//Preprocessor Statements

#include <stdio.h> //header files

#include <reg51.h>

//Main function

void main(void)

{

#define TRUE 1 //symbolic constants

#define FALSE 0

int sum = 0; //Local Declarations

int x;

float y;

//Statements

}

//Global Declarations

unsigned char x,y;

int z;

long n=0;

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Keil Product Downloads

http://www.keil.com/download/product/

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Using Keil

• Open Keil and

start a new project

• Chose a name for

your new project,

create a separate

folder where all

the files of your

project will be

stored, chose a

name and click

save.

Source: http://www.ikalogic.com/part-2-c-programming-for-8051-using-keil-ide/

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Using Keil

• Select a device

for Target ‘Target

1′: seek

for ATMEL, then

select AT89C51,

AT89S52, …

• You will be

asked whether to

‘copy standard

8051 startup

code‘ click No.

Source: http://www.ikalogic.com/part-2-c-programming-for-8051-using-keil-ide/

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Using Keil

• Click File, New

• Click ‘File, Save

as’ and chose a

file name for

your source code

ending with the

letter ‘.c’,

‘code.c’ for

example, and

click save.

Source: http://www.ikalogic.com/part-2-c-programming-for-8051-using-keil-ide/

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Using Keil

Add file to project:

• Right-click on

‘source group 1‘,

click on ‘Add files

to group…‘,

•Right-click on

Target 1,

click Options for

target ‘Target 1′,

then under the

‘Output‘ tab, check

the box ‘crate HEX

file‘.

Source: http://www.ikalogic.com/part-2-c-programming-for-8051-using-keil-ide/ 14

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Using Keil

• Compile your

source code, and

correct eventual

syntax errors:

‘rebuild all

targets’

•Debug:

Source: http://www.ikalogic.com/part-2-c-programming-for-8051-using-keil-ide/ 15

Using Keil

• Run:

• Stop:

• Reset:

• Step:

Source: http://www.ikalogic.com/part-2-c-programming-for-8051-using-keil-ide/ 16

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Keil Variable Extensions

• Declaration of the types of memory

data

internal RAM (direct addressing)

internal RAM (indirect addressing)

bit addressable internal RAM

external data memory

idata

bdata

xdata

code

code memory (program memory)

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data/idata

Description: The variable will be stored in internal data

memory of controller.

Example:

unsigned char data x;

//or

unsigned char idata y;

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bdata

Description: The variable will be stored in bit

addressable memory of controller.

Example:

unsigned char bdata x;

//each bit of the variable x can be accessed

//as follows

x ^ 1 = 1; //1st bit of variable x is set

x ^ 0 = 0; //0th bit of variable x is cleared

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xdata

Description: The variable will be stored in external RAM

memory of controller.

Example:

unsigned char xdata x;

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code

Description: This keyword is used to store a constant

variable in code memory. Lets say you have a big string

which is not going to change anywhere in program.

Wasting ram for such string will be foolish thing. So

instead we will make use of the keyword "code" as

shown in example below.

Example:

unsigned char code str="this is a constant string";

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Variable Types

• The Keil C compiler supports most C variable types and

adds several of its own:

– Standard Types

– Keil Types

• A good understanding of C data types for 8051 can help

programmers to create smaller hex files

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Standard Types

Data type

Bytes Range

unsigned char

signed char

unsigned int

signed int

1

2

4

0 to 255

-128 To +127

0 to 65,535

-32,768 To +32,767

0 to 4,294,967,295

-2,147,483,648 to 2,147,483,647

± 1.175494E-38 to

± 3.402823E +38

unsigned long

signed long

float

4

• Unsigned char is an 8-bit data type in the range of 0 –

255 (00 – FFH) and is one of the most widely used data

types for the 8051.

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Keil Types

Data type

bit

Bits

Bytes

Range

0 to 1

1

sbit

1

0 to 1

sfr

8

1

2

0 to 255

0 to 65,535

sfr16

16

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bit

Description: This keyword is used to define a bit from

bit-addressable on-chip RAM.

Example:

bit = 0x80;

//

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sbit

Description: This keyword is used to define a special bit

from SFR (special function register) memory.

Example:

sbit Port0_0 = 0x80;

// Special bit with name Port0_0 is defined

// at address 0x80

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sfr

Description: sfr is used to define an 8-bit special

function register from SFR memory.

Example:

sfr Port1 = 0x90;

// Special function register with name Port1

// defined at addrress 0x90

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sfr16

Description: This keyword is used to define a two

sequential 8-bit registers in SFR memory.

Example:

sfr16 DPTR = 0x82;

// 16-bit special function register starting

at 0x82

// DPL at 0x82, DPH at 0x83

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unsigned char – Example 1

Source: Chung-Ping Young

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unsigned char – Example 2

Source: Chung-Ping Young

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unsigned char – Example 3

Source: Chung-Ping Young

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signed char – Example

Source: Chung-Ping Young

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sbit, signed int – Example

Source: Chung-Ping Young

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Keywords in Keil C51

• Keil C51 compiler adds few more keywords to the scope

C Language:

_at_

using

large

alien

interrupt

compact

reentrant

small

far

_priority_

_task_

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_at_

Description: This keyword is used to store a variable on

a defined location in ram.

Example:

unsigned char idata x _at_ 0x30;

// variable x will be stored at location

// 0x30 in internal data memory

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using

Description: This keyword is used to define register

bank for a function. User can specify register bank 0 to

3.

Example:

void function () using 2{

// code

}

// Function named "function" uses register

bank 2 while executing its code

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interrupt

Description: This keyword will tells the compiler that function

described is an interrupt service routine. C51 compiler supports

interrupt functions for 32 interrupts (0-31). Use the interrupt

vector address in the following table to determine the interrupt

number.

Interrupt number

Address

0003H

000BH

0013H

001BH

0023H

Interrupt source

External 0

Timer 0

0

1

2

3

4

External 1

Timer 1

Serial

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interrupt

Example:

void External_Int0() interrupt 0{

//code

}

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Examples of Data Types

data char Var1;

char code text [] = "Enter temperature:";

unsigned long xdata MyArray [100];

float idata x, y, z;

unsigned int pdata Dimension;

unsigned char xdata vector [10] [4] [4];

char BDATA Indicator;

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Function

• A general form of a C function looks like this:

<return type> FunctionName (Argument1, Argument2, …)

{

Statement1;

Statement2;

…

}

An example of function:

int sum (int x, int y)

{

int result;

result = x + y;

return (result);

}

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Bài giảng Microprocessing Systems - Chapter 8: C Programming for 8051 - Lê Chí Thông