►Idea Behind Implementation

The basic idea behind PWM implementation on 8051 is using timers and switching port pin high/low at defined intervals. As we have discussed in the introduction of PWM that by changing the Ton time, we can vary the width of square wave keeping same time period of the square wave.

We will be using 8051 Timer0 in Mode 0. Values for high and low level will be loaded in such a way that total delay remains same. If for high level we load a value X in TH0 then for low level TH0 will be loaded with 255-X so that total remains as 255.

►Assembly Code Example

►Timer setup for PWM
	PWMPIN EQU P1.0		; PWM output pin
PWM_SETUP:
	MOV TMOD,#00H		; Timer0 in Mode 0
	MOV R7, #160		; Set pulse width control
	; The value loaded in R7 is value X as
	; discussed above.
	SETB EA		; Enable Interrupts
	SETB ET0		; Enable Timer 0 Interrupt
	SETB TR0		; Start Timer
	RET


►Interrupt Service Routine
TIMER_0_INTERRUPT:
	JB F0, HIGH_DONE	; If F0 flag is set then we just finished
				; the high section of the
LOW_DONE:			; cycle so Jump to HIGH_DONE
	SETB F0			; Make F0=1 to indicate start of high section
	SETB PWMPIN		; Make PWM output pin High
	MOV TH0, R7		; Load high byte of timer with R7
				; (pulse width control value)
	CLR TF0			; Clear the Timer 0 interrupt flag
	RETI			; Return from Interrupt to where
					; the program came from
HIGH_DONE:
	CLR F0			; Make F0=0 to indicate start of low section
	CLR PWMPIN		; Make PWM output pin low
	MOV A, #0FFH	; Move FFH (255) to A
	CLR C			; Clear C (the carry bit) so it does
					; not affect the subtraction
	SUBB A, R7		; Subtract R7 from A. A = 255 - R7.
	MOV TH0, A		; so the value loaded into TH0 + R7 = 255
	CLR TF0			; Clear the Timer 0 interrupt flag
	RETI			; Return from Interrupt to where
				; the program came from


In your main program you need to call this PWM_SETUP routine and your controller will have a PWM output. Timer Interrupt service routine will take care of PWM in the background. The width of PWM can be changed by changing the value of R7 register. In above example I am using 160, you can choose any value from 0 to 255. R7 = 0 will give you o/p 0V approx and R7 = 255 will give you 5V approx.

You can also make use of Timer1 if you want. And the output pin can be changed to whatever pin you want.
►C Code Example

►Timer setup for PWM in C
//Global variables and definition
#define PWMPIN P1_0

unsigned char pwm_width;
bit pwm_flag = 0;

void pwm_setup(){
	TMOD = 0;
	pwm_width = 160;
	EA = 1;
	ET0 = 1;
	TR0 = 1;
}


►Interrupt Service Routine
void timer0() interrupt 1 {
	if(!pwm_flag) {	//Start of High level
		pwm_flag = 1;	//Set flag
		PWMPIN = 1;	//Set PWM o/p pin
		TH0 = pwm_width;	//Load timer
		TF0 = 0;		//Clear interrupt flag
		return;		//Return
	}
	else {	//Start of Low level
		pwm_flag = 0;	//Clear flag
		PWMPIN = 0;	//Clear PWM o/p pin
		TH0 = 255 - pwm_width;	//Load timer
		TF0 = 0;	//Clear Interrupt flag
		return;		//return
	}
}


Now your normal 8051 is capable of PWM output.



◄ Introduction to PWM  |  8051 PWM Example Code  |  AVR PWM Example Code ►

Back to index

Conversation

ExperimenterUK
Thu Oct 30 2014, 06:02 PM
This is a chat box..create a thread if you need help...but we don't do homework
Tue Oct 28 2014, 07:33 PM
vinni
hi rickey...anyone got the pgm...pls gimme now
Tue Oct 28 2014, 06:35 PM
potla
hi vinni even i need that program. help me if you get it
Tue Oct 28 2014, 03:22 PM
vinni
1. Using a look-up table in Flash ROM and accumulator offset indexed addressing mode, write a program that acts as a timer. The timer should count from 0 to 59 seconds. After reaching 59, it should go back to 0 on the next second and continue to count up. The timer should use the seven-segment display. The look-up table should contain information on how to display the digits 0 – 9 on the seven-segment display
Tue Oct 28 2014, 03:22 PM
vinni
hello Rickey..i need this pgm very urgently
Tue Oct 28 2014, 01:42 AM
Boy Donald
Dear sir, thanks before. i have some project urgent for my school and my project need this digital countdown timer using 7 segmen display. but your project only show ten minutes countdown, i need your help, can you show me more to change the minute or set the time manually. thank you, sorry for disturbing you.
Tue Oct 28 2014, 01:32 AM
Boy Donald
dear sir
Tue Oct 28 2014, 01:19 AM
Boy Donald
Rickey you inspired me a lot but why i can not change the time ( minute
Sun Oct 26 2014, 02:51 AM
sandeep bankar
dear sir I m facing problem about..how to read number of incoming call in gsm 900 a. pls help how to read it in atmel avr microcontroller.
ajay_bhargav
Mon Oct 20 2014, 11:22 AM
@skrishna, please post in forum so we can help you better.

Downloads

Comments

prash5054
Thu Oct 30 2014, 06:34 AM
Max.otto
Mon Oct 27 2014, 01:23 PM
toypoy
Sun Oct 26 2014, 01:06 AM
hiswe
Thu Oct 23 2014, 04:18 PM
pddung93
Sun Oct 19 2014, 01:56 PM
msideal
Thu Oct 16 2014, 08:48 AM
robotgirl
Tue Oct 14 2014, 06:23 PM
BRV64
Mon Oct 13 2014, 05:48 AM

Online

Guests: 51, Members: 0 ...

most ever online: 182184
(Members: , Guests: 182184) on 06 Aug 2010: 05:37 AM

Members: 37535
Newest member: prash5054
Forum Activity
rkodaganur Avatar
Posted By rkodaganur
Fri Oct 31 2014, 01:44 AM
Hi Ajay, I wanted to know can we use transformer ...
Max.otto Avatar
Posted By Max.otto
Thu Oct 30 2014, 11:09 AM
Hello all, before generating i have to give PWM p...
prash5054 Avatar
Posted By prash5054
Thu Oct 30 2014, 06:40 AM
can u post the updated code for the above problem ...
ExperimenterUK Avatar
Posted By ExperimenterUK
Wed Oct 29 2014, 05:36 PM
Thank you for the feedback.It's good to hear when ...
msideal Avatar
Posted By msideal
Tue Oct 28 2014, 05:34 PM
ExperimenterUK: Thankyou so much for helping me......
msideal Avatar
Posted By msideal
Tue Oct 28 2014, 05:18 PM
thanks ExperimenterUK for your help.... I will try...
ExperimenterUK Avatar
Posted By ExperimenterUK
Mon Oct 27 2014, 10:29 PM
Your error seems to be the use of PINC, which is f...
msideal Avatar
Posted By msideal
Mon Oct 27 2014, 05:45 PM
i want to extend my i/o's by writing this code. i ...
Max.otto Avatar
Posted By Max.otto
Mon Oct 27 2014, 01:30 PM
Hi all , i am working with PSoC 5LP. I have contin...
gaurav7577 Avatar
Posted By gaurav7577
Mon Oct 27 2014, 09:53 AM
hello everyone i wanna interface blood pressure se...