Assembly language provides direct, low-level control over the 8051's registers and memory. Each assembly instruction typically corresponds to one machine code instruction.

Advantages of Assembly:

• Maximum Performance: Code can be highly optimized for speed and efficiency.
• Minimal Code Size: Generates very compact code, crucial for MCUs with limited program memory.
• Direct Hardware Control: Offers precise control over every bit and register.
• Debugging Low-Level Issues: Essential for understanding exact hardware behavior.

Disadvantages of Assembly:

• Development Time: Slower to write and debug compared to C.
• Portability: Code is not portable to other microcontroller architectures.
• Maintainability: Difficult to read and maintain for complex projects.

This example demonstrates setting up a timer for a delay and then toggling an LED connected to P1.0.

Code snippet

; Program to toggle an LED connected to P1.0 with a 500ms delay
; Crystal Frequency: 11.0592 MHz
; Machine Cycle: 12/11.0592MHz = 1.085 us (approx)
; Desired Delay = 500ms = 500,000 us
; Timer Ticks for 500ms = 500,000 us / 1.085 us/tick = 460830 ticks
; This is too large for a single 16-bit timer (max 65536 ticks).
; We need to generate 50ms delay 10 times to get 500ms.
; Ticks for 50ms = 50,000 us / 1.085 us/tick = 46083 ticks
; TH0:TL0 value for 46083 ticks (Mode 1, 16-bit) = 65536 - 46083 = 19453 (decimal)
; 19453 decimal = 4BFD H
; TH0 = 4BH, TL0 = FDH
ORG 0000H ; Program starts at address 0000H
LJMP MAIN ; Jump to the main program
ORG 000BH ; Timer 0 Interrupt Vector Address
LJMP TIMER0_ISR ; Jump to Timer 0 Interrupt Service Routine
MAIN:
MOV P1, #00H ; Initialize Port 1 (LED is OFF)
SETB P1.0 ; Turn LED ON initially (P1.0 = 1)
; Configure Timer 0 for Mode 1 (16-bit timer)
MOV TMOD, #01H ; Timer 0, Mode 1 (0000_0001B)
; Load initial value for 50ms delay (4BFDH)
MOV TL0, #0FDH
MOV TH0, #04BH
; Enable Timer 0 Interrupt
SETB ET0 ; Enable Timer 0 interrupt
SETB EA ; Enable Global interrupts
; Start Timer 0
SETB TR0 ; Start Timer 0
LOOP:
SJMP LOOP ; Infinite loop, CPU waits for interrupts
; (or perform other tasks while timer runs)
TIMER0_ISR:
CLR TR0 ; Stop Timer 0 (before re-loading)
CLR TF0 ; Clear Timer 0 overflow flag (hardware does this on vector, but good practice)
; Reload Timer 0 for next 50ms delay
MOV TL0, #0FDH
MOV TH0, #04BH
CPL P1.0 ; Complement P1.0 (toggle LED)
SETB TR0 ; Restart Timer 0
RETI ; Return from Interrupt

C is the preferred language for 8051 development due to its readability, maintainability, and greater portability (though specific 8051 extensions are used).

Advantages of C:

• Higher Abstraction: Easier to write and understand complex logic.
• Faster Development Cycle: Reduced coding and debugging time.
• Modularity and Reusability: Code can be easily organized into functions and modules.
• Portability (Limited): More portable than assembly; some code can be reused on other C-supported MCUs.

Disadvantages of C:

• Less Optimal Code Size/Speed: Generated machine code might be larger and slower than hand-optimized assembly.
• Less Direct Control: Compiler might hide some low-level hardware details.

This outlines a C example that toggles an LED on Port P1.0 using a timer to create a delay.

C Code Snippet

#include  // Include standard 8051 register definitions
// Define the LED pin
sbit LED_PIN = P1^0; // P1.0 (Port 1, bit 0)
// Global variable for delay count (if 50ms delay needs to happen multiple times for a longer delay)
unsigned int ms_count = 0;
// Timer 0 Interrupt Service Routine prototype
void Timer0_ISR(void) interrupt 1 // 'interrupt 1' means it's Timer 0 interrupt
{
 // Reload Timer 0 for 50ms delay
 TH0 = 0x4B; // Load high byte
 TL0 = 0xFD; // Load low byte
 ms_count++; // Increment millisecond counter (each increment is 50ms)
 if (ms_count >= 10) // Check if 500ms (10 * 50ms) has passed
 {
 LED_PIN = ~LED_PIN; // Toggle LED
 ms_count = 0; // Reset counter
 }
}
void main()
{
 // --- Configure Timer 0 for 50ms delay ---
 TMOD = 0x01; // Timer 0, Mode 1 (16-bit timer)
 // Load initial value for 50ms delay (4BFDH)
 // 65536 - (50ms / (12 / 11.0592MHz)) = 65536 - 46083 = 19453 (0x4BFD)
 TH0 = 0x4B;
 TL0 = 0xFD;
 // --- Configure Interrupts ---
 ET0 = 1; // Enable Timer 0 Interrupt
 EA = 1; // Enable Global Interrupts
 // --- Start Timer ---
 TR0 = 1; // Start Timer 0
 // Initial LED state
 LED_PIN = 0; // Turn LED OFF initially (assuming active high LED, or low for active low)
 while (1)
 {
 // Main loop, can perform other tasks here while timer runs
 // For this example, it's just an empty loop.
 }
}