►AVR Timers as PWM

Most of AVR controllers have onchip PWM channel which makes PWM usage much simple and more accurate. AVR timers or counters can be used in PWM mode without disturbing the basic timer function.
As in case of AT90S8515, Timer1 can be configured in PWM mode by setting PWM11 and PWM10 bits in TCCR1A register. Following modes are available for PWM:

PWM11PWM10Description
00PWM operation of Timer/Counter1 is disabled
01Timer/Counter1 in 8-bit PWM Mode
10Timer/Counter1 in 9-bit PWM Mode
11Timer/Counter1 in 10-bit PWM Mode

The pre-scalar source for Timer/Counter1 can be selected with the help of clock select bits in TCCR1B register (more information please check datasheet at page 37).

Width of pulse is loaded in the timer output compare registers OCR1A (OCR1AH & OCR1AL) and OCR1B (OCR1BH & OCR1BL). Timer/Counter1 acts as an up/down counter, counting up from $0000 to TOP (see table below), where it turns and counts down again to zero before cycle is repeated. When the counter value matches the content of 10 least significant bits of OCR1A or OCR1B, the PD5 (OC1A)/OC1B pins are set or cleared according to the settings of COM1A1/COM1A0 or COM1B1/COM1B0 bits in Timer/Counter1 Control register (TCCR1A), see table below.

PWM ResolutionTimer Top ValueFrequency
8-bit PWM$00FF (255)Ftck1/510
9-bit PWM$01FF (511)Ftck1/1022
10-bit PWM$03FF (1023)Ftck1/2046


COM1X1COM1X0Effect on OCX1
00Not Connected
01Not Connected
10Cleared on compare match, up-counting. Set on compare match down-counting (non-inverted PWM)
11Cleared on compare match, down-counting. Set on compare match up-counting (inverted PWM)
Note: X = A or B

►Assembly Code Example

;8-bit Non-Inverted PWM code example
.equ pulse_width = $40
;Pulse width can be changed from 0 to TOP
PWM_START:
	ldi temp, pulse_width	;Load pulse width
	out OCR1AL, temp	;OCR1A = Pulse width
	clr temp
	out OCR1AH, temp

	ldi temp, $81		;8-bit PWM Mode
	out TCCR1A, temp	;Non Inverted

	in temp, DDRD		;Make PortD.5 as o/p
	ori temp, (1<<5)
	out DDRD, temp

	ldi temp, $1		;Start PWM
	out TCCR1B, temp
	ret			;Return to main
	;PWM will run in background automatically



►PWM Setup in C
//Global variables and definition
#define PULSE_WIDTH 0x40

void pwm_start(){
	OCR1AL = PULSE_WIDTH;	//Load Pulse width
	OCR1AH = 0;
	DDRD |= (1<<5);		//PortD.5 as o/p
	TCCR1A = 0x81;		//8-bit, Non-Inverted PWM
	TCCR1B = 1;		//Start PWM
}


Most of AVRs have same set of registers for PWM setup. Just go through the datasheet once and configure registers. If you still feel any problem working on things, we are here to help. But please make use of forum


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

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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.

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prash5054
Thu Oct 30 2014, 06:34 AM
Max.otto
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Sun Oct 19 2014, 01:56 PM
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Thu Oct 16 2014, 08:48 AM
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Posted By rkodaganur
Fri Oct 31 2014, 01:44 AM
Hi Ajay, I wanted to know can we use transformer ...
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Posted By Max.otto
Thu Oct 30 2014, 11:09 AM
Hello all, before generating i have to give PWM p...
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Posted By prash5054
Thu Oct 30 2014, 06:40 AM
can u post the updated code for the above problem ...
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Posted By ExperimenterUK
Wed Oct 29 2014, 05:36 PM
Thank you for the feedback.It's good to hear when ...
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Posted By msideal
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ExperimenterUK: Thankyou so much for helping me......
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thanks ExperimenterUK for your help.... I will try...
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Your error seems to be the use of PINC, which is f...
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i want to extend my i/o's by writing this code. i ...
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