►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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Tue Mar 03 2015, 06:59 AM
candyyyy
Hi! Can i ask how do you connect the Vo contrast pin? Do i leave it open?
ExperimenterUK
Sun Mar 01 2015, 07:06 AM
@Anupam Biswas..post all you have done in the GSM forum
Sat Feb 28 2015, 02:51 PM
Anupam Biswas
I am doinga project on gsm based home automation.I have done alittle study about at commands.I am using Atmel 89c51 with yhe gsm module.I am unable to receive any message via the module.The simulation is done on proteus and i am using a virtual terminal.Can anyone please help me?Thanks in advance.
Tue Feb 24 2015, 12:47 AM
MrCurious
is Stat a global variable too? you reference it in Chan's "disk_status" function.
Sat Feb 21 2015, 09:10 PM
Harikumar
കൊള്ളാം
ExperimenterUK
Fri Feb 20 2015, 06:28 AM
@sugikz.. I have asked Ajay about it, he'll soon sort it out
Thu Feb 19 2015, 12:22 PM
sugikz
"Sorry no bots allowed! You entered two different email addresses. Please enter a valid email address in the two fields provided"
Thu Feb 19 2015, 12:21 PM
sugikz
this are the problem notice box;
Thu Feb 19 2015, 12:20 PM
sugikz
yes, i still got stuck on email problem, i've used gmail, yahoo, and told some friends of mine to sign up on the site, but they face the same problem as iam,
Thu Feb 19 2015, 05:48 AM
sjeeva
hi, is any doing a project on raspberry pi

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Tue Mar 03 2015, 04:32 PM
Dear All ,can you help me to solve the regarding t...
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