8051 program – pwm

Pulse width modulation is basically a square wave with a varying high and low time.
On-Time (T_on): Duration of time signal is high
Off-Time (T_off): Duration of time signal is low
Period (T_total): It is represented as the sum of on-time and off-time of PWM signal
Duty cycle: It is represented as percentage of time signal remains on during the period of the PWM signal. Duty cycle is calculated as on-time to the period of time.
D = T_on / T_total

; pwm generation
; standard 8051, 12MHz XTAL
; 1KHz square wave with 50% duty cycle on P1.0
; Timer 0, 16-bit mode
	ORG 0H
	MOV P1,#00000000B
	MOV TMOD,#00000001B
PWM:
	SETB P1.0
	ACALL DELAY
	CLR P1.0
	ACALL DELAY
	SJMP PWM
DELAY:		; 500us
	MOV TH0,#0FEH
	MOV TL0,#00CH
	SETB TR0
HERE:
	JNB TF0,HERE
	CLR TR0
	CLR TF0
	SETB P1.0
	RET
	END

; pwm generation
; standard 8051, 12MHz XTAL
; 1KHz square wave with 10% duty cycle on P1.0
; Timer 0, 16-bit mode
	ORG 0H
	MOV P1,#00000000B
	MOV TMOD,#00000001B
PWM:
	SETB P1.0
	MOV R0, #0FFH
	MOV R1, #9CH
	ACALL DELAY	; 100us
	CLR P1.0
	MOV R0, #0FCH
	MOV R1, #7CH
	ACALL DELAY	; 900us
	SJMP PWM
DELAY:
	MOV TH0,R0
	MOV TL0,R1
	SETB TR0
HERE:
	JNB TF0,HERE
	CLR TR0
	CLR TF0
	SETB P1.0
	RET
	END

; pwm generation
; standard 8051, 12MHz XTAL
; 1KHz square wave with 70% duty cycle on P1.0
; Timer 0, 16-bit mode
	ORG 0H
	MOV P1,#00000000B
	MOV TMOD,#00000001B
PWM:
	SETB P1.0
	MOV R0, #0FDH
	MOV R1, #44H
	ACALL DELAY	; 700us
	CLR P1.0
	MOV R0, #0FEH
	MOV R1, #0D4H
	ACALL DELAY	; 300us
	SJMP PWM
DELAY:
	MOV TH0,R0
	MOV TL0,R1
	SETB TR0
HERE:
	JNB TF0,HERE
	CLR TR0
	CLR TF0
	SETB P1.0
	RET
	END

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List of topics: 8051

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