►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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Sat Jan 31 2015, 11:17 AM
Pradeep Singh
I'm using 8051 microcontroller and want to configure HC-06 with it but I'm not able to find out what problem is occuring as my blueethooth is getting connected but no communication between blwutooth and pc/andriod phone
sachinmm
Sat Jan 31 2015, 05:23 AM
hello sir,i ask the question related to 7 segment display plz help me.
Thu Jan 29 2015, 11:24 AM
durai
I found discussion relevant to my problem (link:http://www.8051projects.net/t59199/gsm-cdma-discussion/flashing-new-firmware-in-sim900-modem.htm) but i could not find the project mentioned in that discusion
Thu Jan 29 2015, 11:21 AM
durai
Hi i am using a SIM/900A GSM modem, I want to send email with an attachement using a microcontroller but when i try to use AT_Email commands it gives me error,I think modem doesnot support those commands,is there any other way to send mail using that modem??
ajay_bhargav
Thu Jan 29 2015, 06:54 AM
@gaurav, please mail me message you're trying to post.
ExperimenterUK
Thu Jan 29 2015, 01:17 AM
bhagyesh.bhavasar/gaurav.k I can post with Firefox. Can you try other browsers ?
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Wed Jan 28 2015, 08:08 AM
the web theme is too much buggy and heavy , admin please change it to simple theme, so that user can browse quickly
naqirizvi
Wed Jan 28 2015, 08:07 AM
some one please share software name or ebooks related to avr
bhagyesh.bhavasar
Tue Jan 27 2015, 11:06 AM
i want to share my project but there is problem occurred during postng
bhagyesh.bhavasar
Tue Jan 27 2015, 05:58 AM
@ExperimentalUK i have used that purple button but same as previous it takes me to blank page

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hello sir, plz tell me the circuit diagram interfa...
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