Paja

Arduino NG supports PWM with three pins – 9, 10 and 11. Those pins are assigned to Atmega8 PB1(OC1A), PB2(SS/OC1B) and PB3(MOSI/OC2) pings

PB1 (OC1A) – Arduino Pin 9

PB2(OC1B) – Arduion Pin 10

PB3(MOSI/OC2) – Arduion Pin 11

TCCR1A (Timer/Counter 1 Control Register A) and TCCR1B (Timer/Counter 1 Control Register B)

TCCR1A and TCCR1B  are registers to configure PWM function.

TCCR1A Bit	7	6	5	4	3	2	1	0
	COM1A1	COM1A0	COM1B1	COM1B0	–	–	PWM11	PWM10

TCCR1A Bit	Name	Meaning	Opportunities
7	COM1A1	Compare Output A	00: OC1A/B not connected 01: OC1A/B changes polarity 10: OC1A/B to zero 11: OC1A/B to one
6	COM1A0
5	COM1B1	Compare Output B
4	COM1B0
3	(not used)
2
1	PWM11	Pulse with modulator (analog output)	00: PWM off 01: 8-Bit PWM (0 – 255) 10: 9-Bit PWM (0 – 511) 11: 10-Bit PWM (0 – 1023)
0	PWM10

Example code:

TCCR1A = (1<<COM1A1)|(1<<PWM0);     //  Non-Inverted PWM, 8-Bit PWM

TCCR1B Bit	7	6	5	4	3	2	1	0
	ICNC1	ICES1	–	–	CTC1	CS12	CS11	CS10

TCCR1B Bit	Name	Meaning	Opportunities
7	ICNC1	Input Capture 1 Noise Canceller (4CKs)	0: Noise Canceller disabled 1: Voltage change on ICP must last at least 4 clock cycles
6	ICES1	Input Capture 1 Edget Select	0: Falling edge on ICP triggers T/C1 capure 1: Rising edge on ICP triggers T/C1 capture
5	–
4	–
3	CTC1	Clear Timer/Counter1 on Compare Match	0: Doesn’t reset T/C1 on Compare Match 1: T/C1 is reset to $0000 on Compare Match
2	CS12	ADC Channel Select	000: STOP! T/C1 is stopped 001: T/C1 counts at the clock speed (CK) 010: T/C1 counts at CK/8 011: T/C1 counts at CK/64 100: T/C1 counts at CK/256 101: T/C1 counts at CK/1024 110: T/C1 counts on falling edget of T1 pin 111: T/C1 counts on rising edge of T1 pin
1	CS11
0	CS10

Example code:

TCCR1B = (1<<CS10);             //Start PWM

OCR1A (Timer/Counter 1 Output Compare register A) 16 bit register

OCR1A is a 16 bit register to store value of PWM. Highbyte of OCR1A can be acessed by using OCR1AH and lowbyte by OCR1AL. If PWM is set as 8-bit PWM, highbyte of OCR1AH is not used.

OCR1AH (Highbyte) 8 bit
OCR1AL (Lowbyte)  8 bit

OCR1A Bit	7	6	5	4	3	2	1	0
	–	–	–	–	–	–	–	–

Example code:

for (i=0; i<255; i++) {

OCR1AL = i;         //Change lowbyte of OCR1A

_delay_ms(10);

}

Dimming LED

#include <avr/io.h>

#include <util/delay.h>

int main(void)

{

OCR1AH = 0;

DDRB |= (1<<PB1);         //PortB 1 as output

TCCR1A = (1<<COM1A1)|(1<<1);   // OC1A to zero, 8-Bit PWM

TCCR1B = 1;             //Start PWM

for (;;) {

int i;

for (i=0; i<255; i++) {

OCR1AL = i;         //Change lowbyte of OCR1A

_delay_ms(10);

}

for (i=255; i>0; i–) {

OCR1AL = i;

_delay_ms(10);

}

}

return 0;   //  never reached

}