8051 Interface - LED

In this 8051 Interface LED tutorial, you will learn how to implement a “Hello World” LED Blinking project in Keil for a microcontroller. Additionally, we have chosen the AT89S51 microcontroller (although you can select any other microcontroller supported by Keil) for demonstration purposes. This project is straightforward and can be easily followed by the steps outlined below.

Light Emitting Diodes (LEDs) are fundamental and widely used electronic components for displaying digital signal states. When current flows through an LED, it emits light. However, excessive current can damage it; therefore, a current-limiting resistor is necessary. Commonly used resistors for this purpose include 220, 470, and 1K ohms. Depending on the desired brightness, any of these resistors can be utilized. Let’s begin by blinking LEDs; subsequently, we can proceed to generate various patterns using the available LEDs.

An essential aspect of any controller is the number of General Purpose Input/Output (GPIO) pins available for connecting peripherals. The 8051 microcontroller features 32 GPIOs organized into four ports, namely P0 to P3.

Contents

1 Required software
2 Required components and Programmer
3 Circuit Diagram
4 C code
5 C Code Explanation
6 Assembly Code
7 Assembly Code Explanations
- 7.1 Table 1: Instructions from Address 0000 to 082B
- 7.2 Table 2: Instructions from Address 081D to 0834
8 NEXT
- 8.1 Explore more

Required software

Windows machine (Any Version)
Keil IDE tool for 8051
ProgISP v1.72

Required components and Programmer

1x AT89S51 Controller
1x 4Mhz Crystal
2x 22pf capacitor
1x LED 5v
ISP AVR USB programmer

Circuit Diagram

C code

See on GitHub AEW_Blink_LED.c

// http://esp8266iot.blogspot.in/
// http://aruneworld.blogspot.com/
// Tested By 	: Arun(20170227)
// Example Name : AEW_Blink_LED.lua

// Program to blink an LED at Port pin P1.0 (physical pin 1 of IC)

#include<reg52.h>  // special function register declarations for 89s52                

#include<stdio.h>  // prototype declarations for I/O functions

sbit LED = P1^1;    // defining pin P1^0 as LED

void delay(void) ;  //delay function prototype declaration

void main (void)
   
{
    LED = 0 ;              // Make LED pin as Output
    while(1)                //indefinite loop
    {
       LED = 0;           // LED Off
       delay();
       LED = 1;          // LED ON 
       delay();
    }
}

void delay(void)
{
    int j;
    int i;
    for(i=0;i<10;i++)
    {
        for(j=0;j<10000;j++)
        {
        }
    }
}

C Code Explanation

This table breaks down each line of the code along with its explanation to provide a clear understanding of the functionality of each part of the program.

Line No.	Code	Explanation
1-5	`// http://esp8266iot.blogspot.in/ // http://aruneworld.blogspot.com/ // Tested By : Arun(20170227) // Example Name : AEW_Blink_LED.lua`	Comments providing information about the code, including source references, testing details, and example name.
7	`#include<reg52.h>`	Includes the header file `reg52.h`, which contains special function register declarations for the AT89S52 microcontroller.
9	`#include<stdio.h>`	Includes the standard I/O header file `stdio.h`, although it seems unnecessary in this code since there are no standard I/O functions used.
11	`sbit LED = P1^1;`	Declares a bit-specific variable named `LED`, representing pin P1.1. This syntax is specific to the 8051 family of microcontrollers.
13-24	`void delay(void) ;`	Function prototype declaration for `delay()`.
26-35	`void main (void)`	Main function declaration.
28	`LED = 0 ;`	Configures the LED pin as an output by setting it to 0.
29-33	`while(1)`	Initiates an infinite loop to ensure the LED continues blinking indefinitely.
30	`LED = 0;`	Turns off the LED.
31	`delay();`	Calls the `delay()` function to introduce a delay.
32	`LED = 1;`	Turns on the LED.
33	`delay();`	Calls the `delay()` function again to introduce another delay.
37-47	`void delay(void)`	Function definition for `delay()`.
39-46	`int j; int i; for(i=0;i<10;i++) { for(j=0;j<10000;j++) { } }`	Nested loops to generate a time delay. The outer loop iterates 10 times, and the inner loop iterates 10,000 times, creating an approximate delay.

Assembly Code

See on GitHub AEW_Blink_LED.asm

      ORG 0000H
0000| 	LJMP 082BH 
      ORG 0800H
0800| 	CLR A
0801| 	MOV R7,A
0802| 	MOV R6,A
0803| 	CLR A
0804| 	MOV R5,A
0805| 	MOV R4,A
0806| 	INC R5
0807| 	CJNE R5,#00H,01H
080A| 	INC R4
080B| 	CJNE R4,#27H,0F8H
080E| 	CJNE R5,#10H,0F5H
0811| 	INC R7
0812| 	CJNE R7,#00H,01H
0815| 	INC R6
0816| 	MOV A,R7
0817| 	XRL A,#0AH
0819| 	ORL A,R6
081A| 	JNZ 0E7H
081C| 	RET
081D| 	CLR 91H
081F| 	CLR 91H
0821| 	LCALL 0800H
0824| 	SETB 91H
0826| 	LCALL 0800H
0829| 	SJMP 0F4H
082B| 	MOV R0,#7FH
082D| 	CLR A
082E| 	MOV @R0,A
082F| 	DJNZ R0,0FDH
0831| 	MOV 81H,#07H
0834| 	LJMP 081DH
      	END

Assembly Code Explanations

These tables provide a clear separation of the instructions, making it easier to read and understand each part of the code.

Table 1: Instructions from Address 0000 to 082B

Address	Code	Mnemonic	Description
0000	LJMP 082BH	LJMP	Long Jump to address 082Bh
0800	CLR A	CLR	Clear Accumulator (A)
0801	MOV R7,A	MOV	Move Accumulator (A) to Register 7 (R7)
0802	MOV R6,A	MOV	Move Accumulator (A) to Register 6 (R6)
0803	CLR A	CLR	Clear Accumulator (A)
0804	MOV R5,A	MOV	Move Accumulator (A) to Register 5 (R5)
0805	MOV R4,A	MOV	Move Accumulator (A) to Register 4 (R4)
0806	INC R5	INC	Increment Register 5 (R5)
0807	CJNE R5,#00H,01H	CJNE	Compare and Jump if Not Equal; Compare R5 to 00H, if not equal, jump to address 01H
080A	INC R4	INC	Increment Register 4 (R4)
080B	CJNE R4,#27H,0F8H	CJNE	Compare and Jump if Not Equal; Compare R4 to 27H, if not equal, jump to address 0F8H
080E	CJNE R5,#10H,0F5H	CJNE	Compare and Jump if Not Equal; Compare R5 to 10H, if not equal, jump to address 0F5H
0811	INC R7	INC	Increment Register 7 (R7)
0812	CJNE R7,#00H,01H	CJNE	Compare and Jump if Not Equal; Compare R7 to 00H, if not equal, jump to address 01H
0815	INC R6	INC	Increment Register 6 (R6)
0816	MOV A,R7	MOV	Move Register 7 (R7) to Accumulator (A)
0817	XRL A,#0AH	XRL	Exclusive OR with Immediate; Perform exclusive OR operation between A and 0AH
0819	ORL A,R6	ORL	Logical OR between Accumulator (A) and Register 6 (R6)
081A	JNZ 0E7H	JNZ	Jump if Not Zero; Jump to address 0E7H if the result of the previous operation is not zero
081C	RET	RET	Return from Subroutine

Table 2: Instructions from Address 081D to 0834

Address	Code	Mnemonic	Description
081D	CLR 91H	CLR	Clear the content of memory address 91H
081F	CLR 91H	CLR	Clear the content of memory address 91H
0821	LCALL 0800H	LCALL	Long Call to subroutine at address 0800H
0824	SETB 91H	SETB	Set the content of memory address 91H
0826	LCALL 0800H	LCALL	Long Call to subroutine at address 0800H
0829	SJMP 0F4H	SJMP	Short Jump to address 0F4H
082B	MOV R0,#7FH	MOV	Move Immediate to Register; Move the value 7FH to Register 0 (R0)
082D	CLR A	CLR	Clear Accumulator (A)
082E	MOV @R0,A	MOV	Move Accumulator (A) to the memory location pointed by Register 0 (R0)
082F	DJNZ R0,0FDH	DJNZ	Decrement and Jump if Not Zero; Decrement Register 0 (R0) and if the result is not zero, jump to address 0FDH
0831	MOV 81H,#07H	MOV	Move Immediate to Register; Move the value 07H to the memory location pointed by Register 1 (81H)
0834	LJMP 081DH	LJMP	Long Jump to address 081DH