![]() ![]() ![]() This corresponds to mode 1 on Table 13-4 above. This means only WGM10 is set and the rest is clear. Looking at wiring.c, we see this: #if defined(TCCR1A) & defined(WGM10) The combination of WGM13:10 bits and what mode they represent is on table 13-4: Moreover, COM1A1 and COM1A0 is also on TCCR1A. These bits are in the TCCR1A (bits 1 and 0) and TCCR1B (bits 4 and 3) registers respectively. The combination to use depends on what mode the Timer1 is in.īits WGM13, WMG12, WGM11 and WGM10 configure the mode. Settings for Channel A requires manipulating a pair of bits, COM1A1 and COM1A0. For simplicity, let’s focus on Channel A (output on D9). Channel A is OC1A or digital pin 9 and Channel B is OC1B is or digital pin 10. There are two channels (and pin) that we can use with Timer1. We wouldn't know what this mean unless we know what mode Timer1 is on. Then we see that COM1A1 is set: sbi(TCCR1A, COM1A1) The #if #endif here makes the code safe for Arduino boards that might not have a Timer1 timer. Going back on the snippet above, we see this part: #if defined(TCCR1A) & defined(COM1A1) Here, I will focus on the 16-bit Timer1 timer. ![]() I recommend you read Secrets of Arduino PWM for an explanation on how PWM is generated for the 8-bit timers. Of course, this is not the case for the 16-bit Timer1. only the low byte will be read for values beyond 255). However the OCRxx registers for both Timer0 and Timer2 are 8-bit registers so passing a value beyond 255 will mess up PWM generation (e.g. The value 30000 passes to the corresponding OCRxx register. So there’s nothing wrong when we do this: analogWrite(9, 30000) The digitalPinToTimer() function determines which timer is for the given pin. Note that you can still write beyond 255 since after this, an else statement is found: switch(digitalPinToTimer(pin)) This means writing 0 to value just clears the pin while writing 255 sets the pin. Interestingly, the function takes values zero and 255 as extremes: if (val = 0) The rest of the code is just the same bits repeating for the other timers on other Arduino boards. connect pwm to pin on timer 1, channel B connect pwm to pin on timer 1, channel A connect pwm to pin on timer 0, channel B connect pwm to pin on timer 0, channel A Here’s some part of the function: void analogWrite(uint8_t pin, int val) ![]() The function definition resides on wiring_analog.c on the Arduino core. To answer the question above, we will look at how analogWrite() is implemented. Will this do anything? Dissecting the AnalogWrite Function Here, we set the value parameter to 30000 which is obviously beyond 255 but within the limits of the int variable. This one uses Timer1 but is this possible? analogWrite(9, 30000) While this uses Timer2: analogWrite(11, 100) So this uses Timer0: analogWrite(5, 100) In fact, the timer used depends on the PWM pin you specify: The Arduino UNO contains three timers: two 8-bit (Timer0 and Timer2) and one 16-bit (Timer1). However, the documentation specifies that the value parameter must be between 0 and 255, which makes it essentially an 8-bit variable. Both parameters are of int type, a 16-bit data type. The function accepts two parameters: pin and value and returns nothing. Most of us are familiar with Arduino’s analogWrite() function in generating PWM: analogWrite(pin, value) The most common are dimming a LED or controlling the speed of a DC motor. PWM has a lot of uses in the microcontroller world. Ever since I wrote about timer interrupts, a number of readers have asked me on how to generate a 16-bit pulse width modulation (PWM) signal with Arduino. ![]()
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