8/20/2019 Arduino Mega Pwm
On the Arduino Mega, it works on pins 2 - 13 and 44 - 46. Older Arduino boards with an ATmega8 only support analogWrite on pins 9, 10, and 11. The Arduino Due supports analogWrite on pins 2 through 13, and pins DAC0 and DAC1. Unlike the PWM pins, DAC0 and DAC1 are Digital to Analog converters, and act as true analog outputs. Arduino and PWM. The Arduino IDE has a built in function “analogWrite” which can be used to generate a PWM signal. The frequency of this generated signal for most pins will be about 490Hz and we can give the value from 0-255 using this function. AnalogWrite(0) means a signal of 0% duty cycle. AnalogWrite(127) means a signal of 50% duty cycle.
Description
Writes an analog value (PWM wave) to a pin. Can be used to light a LED at varying brightnesses or drive a motor at various speeds. After a call to
analogWrite() , the pin will generate a steady square wave of the specified duty cycle until the next call to analogWrite() (or a call to digitalRead() or digitalWrite() ) on the same pin.
* In addition to PWM capabilities on the pins noted above, the MKR and Zero boards have true analog output when using
analogWrite() on the DAC0 (A0 ) pin.** In addition to PWM capabilities on the pins noted above, the Due has true analog output when using analogWrite() on pins DAC0 and DAC1 .
You do not need to call
pinMode() to set the pin as an output before calling analogWrite() .The analogWrite function has nothing to do with the analog pins or the analogRead function.
SyntaxParameterspin : the Arduino pin to write to. Allowed data types: int .value : the duty cycle: between 0 (always off) and 255 (always on). Allowed data types: int .
Returns
I'm trying to enable a PWM on an Arduino Mega (ATmega2560), but I'm facing to some issues.
First, I'm trying to program this in Ada. I desire to use the three Timer3 channels with FastPWM, so I wrote
The hardware connections are OK; I tested it using simple code on the Arduino IDE. So for me it's very clear that the code is lacking something or making something wrong, and this should be caused by an issue in PWM initialization. Could someone explain me where did I make such a mistake?
Thanks in advance.
Update
If Ada can be difficult to get the whole logic, the equivalent code in C is (you can build it using AS6, the result is the same, i.e., no signal is generated):
RegoRego
4 Answers![]()
Looking at www.atmel.com/Images/doc2549.pdf page 136, I see a note:
'The Power Reduction Timer/Counter3 bit, PRTIM3, in “PRR1 – Power Reduction Register 1” onpage 57 must be written to zero to enable Timer/Counter3 module.'
May be relevant?
I don't know what the defaults are for the power management regs, and I haven't used the 2560.
The rest looks OK to me, though I have used the timer libraries avr-timer0.adb etc on the 328p instead of rolling my own.
Brian DrummondBrian Drummond
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I'm not sure, but if you forget the endless loop at the end of your main function, the program stops, all interrupts will be disabled and the controllers enters an empty loop.
And without interrupts no PWM.
MaikMaik
You need to set SEI flag in SREG to enable interrupts and add endless loop in main. Avr programs doesn't terminate or hang after reaching end of main function, but start it all over again. http://www.atmel.com/webdoc/avrassembler/avrassembler.wb_SEI.html
Hubert BossyHubert Bossy
One observation pops out at once -- almost sure this isn't right:
Why? Because the named constants like
COM3A0 are just aliases for integers which indicate bit position (0 to 7). In C, when we set these we do something like:
and COM3A0 = 3, then it becomes (1<<3), or 8 that is ORed.
Which shifts a 1 the number of places leftward before ORing it with the current register value. So unless your COM3A0 for example is already bit-shifted, all this statement is doing is ORing several ones and zeroes and assigning the single result to TCCR3A.
TomServoTomServo
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