8051 Microcontroller

; Sample 8051 Assembly Program
ORG 0000H       ; Start at address 0000H
LJMP MAIN     ; Jump to main program

ORG 0030H       ; Main program starts here
MAIN:
    MOV A, #55H   ; Load 55H into accumulator
    MOV P1, A     ; Output to Port 1
    ACALL DELAY   ; Call delay subroutine
    MOV A, #0AAH
    MOV P1, A
    ACALL DELAY
    SJMP MAIN    ; Repeat forever

DELAY:
    MOV R0, #0FFH ; Delay subroutine
DELAY_LOOP:
    DJNZ R0, DELAY_LOOP
    RET
    
END

// Blink LED on P1.0
#include <reg51.h>
#include <stdio.h>

void delay(unsigned int time) {
    unsigned int i,j;
    for(i=0;i<time;i++)
        for(j=0;j<1275;j++);
}

void main() {
    while(1) {
        P1_0 = 1;    // LED ON
        delay(1000);
        P1_0 = 0;    // LED OFF
        delay(1000);
    }
}

// Timer 0 as interval timer (Mode 1)
#include <reg51.h>

void timer0_isr() interrupt 1 {
    TH0 = 0x3C;    // Reload for 50ms @ 11.0592MHz
    TL0 = 0xB0;
    P1_0 = ~P1_0;  // Toggle pin
}

void main() {
    TMOD = 0x01;   // Timer 0, Mode 1
    TH0 = 0x3C;    // Initial values
    TL0 = 0xB0;
    TR0 = 1;       // Start timer
    ET0 = 1;       // Enable timer interrupt
    EA = 1;        // Global interrupt enable
    
    while(1);      // Infinite loop
}

// Serial Echo Program
#include <reg51.h>

void serial_isr() interrupt 4 {
    if (RI) {
        RI = 0;            // Clear receive flag
        SBUF = SBUF;       // Echo received byte
        while(!TI);      // Wait for transmit
        TI = 0;            // Clear transmit flag
    }
}

void main() {
    TMOD = 0x20;   // Timer 1, Mode 2 (auto-reload)
    TH1 = 0xFD;    // 9600 baud @ 11.0592MHz
    SCON = 0x50;   // Serial Mode 1, enable reception
    TR1 = 1;       // Start timer
    ES = 1;        // Enable serial interrupt
    EA = 1;        // Global interrupt enable
    
    while(1);      // Infinite loop
}