; Program: LED Control with PB0 and PB1
; Microcontroller: PIC16F877A
; Function: PB0 -> LED OFF, PB1 -> LED ON
 
    LIST P=16F877A          ; Specify the PIC16F877A microcontroller
    INCLUDE <P16F877A.INC>  ; Include file for register definitions
 
    __CONFIG _XT_OSC & _WDT_OFF & _PWRTE_ON & _BODEN_OFF & _LVP_OFF
 
; Start of code
    ORG 0x0000              ; Reset vector
    GOTO MAIN               ; Jump to main program
 
    ORG 0x0004              ; Interrupt vector
    GOTO ISR                ; Jump to interrupt service routine
 
; Main Program
MAIN:
    BCF STATUS, RP0         ; Select Bank 0
    CLRF PORTB              ; Clear PORTB output
    CLRF TRISB              ; Configure PORTB as output
    BSF STATUS, RP0         ; Switch to Bank 1
    BSF TRISB, 0            ; Set RB0 (PB0) as input
    BSF TRISB, 1            ; Set RB1 (PB1) as input
    BCF STATUS, RP0         ; Return to Bank 0
 
    BSF INTCON, INTE        ; Enable external interrupt on RB0
    BSF INTCON, GIE         ; Enable global interrupts
 
MAIN_LOOP:
    GOTO MAIN_LOOP          ; Infinite loop
 
; Interrupt Service Routine (ISR)
ISR:
    BTFSC PORTB, 0          ; Check if PB0 (RB0) is pressed
    GOTO LED_OFF            ; Turn LED off if PB0 is pressed
    BTFSC PORTB, 1          ; Check if PB1 (RB1) is pressed
    GOTO LED_ON             ; Turn LED on if PB1 is pressed
 
    BCF INTCON, INTF        ; Clear the external interrupt flag
    RETFIE                  ; Return from ISR
 
LED_OFF:
    BCF PORTB, 7            ; Turn off LED (clear RB7)
    BCF INTCON, INTF        ; Clear interrupt flag
    RETFIE                  ; Return from ISR
 
LED_ON:
    BSF PORTB, 7            ; Turn on LED (set RB7)
    BCF INTCON, INTF        ; Clear interrupt flag
    RETFIE                  ; Return from ISR
 
    END                     ; End of program
 

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