Timer Interrupt Handling

This program demonstrates interrupt handling using Timer 0 overflow interrupt on the 8051.

Description link

The program uses Timer 0 in auto-reload mode. When the timer overflows, it generates an interrupt that toggles a pin (P2.1). Meanwhile, the main program continuously copies data from Port 0 to Port 1.

Code link

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ORG 0000H
	LJMP MAIN
	ORG 00BH
		CPL P2.1
		RETI
	ORG 0030H
	MAIN: 
	MOV TMOD , #00000010B
	MOV IE , #10000010B;
	
	SETB TR0
	BACK:
		MOV A , P0;
		MOV P1,A;
		SJMP BACK
END

Explanation link

Interrupt Vector Table link

• ORG 0000H: Reset vector - jumps to main program
• ORG 00BH: Timer 0 overflow interrupt vector

Interrupt Service Routine (ISR) link

• CPL P2.1: Toggle P2.1 pin
• RETI: Return from interrupt

Main Program link

1. MOV TMOD, #00000010B: Configure Timer 0 in mode 2 (8-bit auto-reload)
2. MOV IE, #10000010B: Enable interrupts
   • Bit 7 = 1: Global interrupt enable (EA)
   • Bit 1 = 1: Timer 0 interrupt enable (ET0)
3. SETB TR0: Start Timer 0
4. BACK loop: Main task - copy Port 0 to Port 1

The timer generates periodic interrupts, and P2.1 toggles on each overflow while the main program continues running.