►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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ajay_bhargav
Mon Mar 23 2015, 04:22 AM
You can only simulate simple 8051. RD2 support is not there in proteus. However there are similar atmel varient which can be used instead.
Sun Mar 22 2015, 07:24 PM
Aryan Nath
How can i Simulate microcontroller project in Proteus that uses P89V51RD2
Thu Mar 19 2015, 02:45 PM
Peter Mann
I have tried to register on the site, but it keeps saying I've entered two different email adresses - but I haven't!
ajay_bhargav
Sun Mar 15 2015, 08:25 PM
I did not get new message indication.. strange..
ExperimenterUK
Sun Mar 15 2015, 08:18 PM
slight delay, my connection failed
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Atleast you chat on our website if not anywhere else
ajay_bhargav
Sun Mar 15 2015, 08:08 PM
Hi Phil..
ExperimenterUK
Sun Mar 15 2015, 08:05 PM
Hi Ajay
gsdvprasad
Fri Mar 13 2015, 04:20 PM
Can you help me how to change the text on led display in proteus simulation?
ajay_bhargav
Sat Mar 07 2015, 07:48 AM
@Shoukat, its general purpose PCB board for soldering components

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Posted By iamalien
Sat Mar 28 2015, 04:48 AM
To answer it as vaguely as the question, you just ...
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Posted By iamalien
Sat Mar 28 2015, 04:27 AM
i thought that lighting led for more times should ...
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Posted By mayank058
Fri Mar 27 2015, 06:46 AM
Dear Sir, I am working on MCB2300. I...
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Thu Mar 26 2015, 09:06 PM
Have a look through the list of projects in our do...
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As you say, each column is only on for part of the...
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Hello guys, i am doing a project on display using ...
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Thank you sir I make a try with the transducer and...
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Tue Mar 24 2015, 05:32 PM
There would be no any biasing circuit?only a shunt...
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Tue Mar 24 2015, 04:55 PM
Your suggestion worked Mr. ExperimenterUK. I tried...