#ARDUINO ANALOGWRITE VS CLOCK OUTPUT PWM CODE#

#ARDUINO ANALOGWRITE VS CLOCK OUTPUT PWM CODE#

The original source code supports many tips using #if’s. Only the source code for Arduino UNO is quoted. The analogWrite() is defined in hardware/arduino/avr/cores/arduino/wiring_analog.c as below. The analogWrite() dose not set it but the tone() uses it. If TCNT2 becomes 0, the output becomes HIGH. When using Phase Correct PWM, comparing TCNT2 with OCR1A or OCR1B, if they are the same value, the output becomes LOW. They hold duty ratio specified by analogWrite(). The OCR2A(for pin 11) and OCR2B(for pin 3)are 8bit compare registers. If it goes to 255 then it decrements the counter to 0. The TCNT2 is an eight bit register and timer/counter. $$f = clock frequency / (division ratio imes 255 imes 2)$$Īs the clock frequency is 16 MHz and the division ratio is 64, the PWM frequency of the PWM output to digital pin 11 and pin 3 is, 16000000 / (64 * 255 * 2) = 490.1961 Hz. In case of the Arduino UNO, the init() function sets CS22 to 1. The TCCR2A(timer/counter 2 control register A) and TCCR2B(timer/counter 2 control register B) control the PWM output. The timer/counter 2 controls the PWM output of digital pins 3(related to OC2B) and 11(related to OC2A). It is controlled by register named TCCR2A, TCCR2B, TCNT2, OCR2A, OCR2B, TIMSK2, TIFR2 ASSR and GTCCR. The analogWrite() dose not use ICR1H/ICR1L, TIMSK1, and TIFR1. The figure below depicts how Phase Correct PWM works.

If TCNT1 becomes 0, the output becomes HIGH. When using Phase Correct PWM, comparing TCNT1H/TCNT1L with OCR1A or OCR1B, if they are the same value, the output becomes LOW. The combination of OCR1A(for pin 9) and OCR1B(for pin 10) is a 16bit compare registers. In case of the Arduino Uno, It is used as a 8bit counter because it increments from 0 to 255 then decrement from255 to 0. The TCNT1H and TCNT1L are 8bit counters and the combination of the two is used as a 16 bit counter. As the clock frequency is 16 MHz and the division ratio is 64, the PWM frequency of the PWM output to digital pin 9 and pin 10 is, 16000000 / (64 * 255 * 2) = 490.1961 Hz. The value of TOP is 255 when using phase correct PWM 8bit. $$ f = clock frequency / (division ratio * TOP * 2)$$ The frequency of the Phase Correct PWM is calculated as follows. In case of the Arduino UNO, the init() function sets CS11 and CS10 to 1. The figure below depicts how fast PWM works. If TCNT0 becomes 0, the output becomes HIGH. When using fast PWM, comparing TCNT0 with OCR0A or OCR0B, if they are the same value, the output becomes LOW. The OCR0A(for pin 6) and OCR0B(for pin 5)are 8bit compare registers.

The TCNT0 is an eight bit register and timer/counter. The clock frequency is 16MHz and the division ratio is 64, the frequency of wave output to the digital pin 5 and 6 is 16000000 / (64 * 256) = 976.5625 Hz. $$f = clock frequency / (division ratio * 256)$$ The frequency of the Fast PWM is calculated as follows. In case of the Arduino Uno, the init() sets the CS01 and CS00 to 1. Clock on falling edge.Įxternal clock source on T0 pin.

Arduino analogwrite vs clock output pwm