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Why only selective pins have PWM ?

rishi2628

For atmega328p ,there are only 6 pins that have the function of pwm. PWM is basically oscillating the pin high to low where the width of the high pulse decides the value of the signal. This can also be done manually by keeping the pin high for few microseconds and then low for some more microseconds. I tried controlling a pwm servo from a non pwm pin using this logic and it worked. So now coming to the question, if high and low is what is there to pwm then why is it only limited to 6 pins. All the I/O pins of atmega328p should have the pwm facility but why only 6 have this facility? What makes these 6 pins so special?

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    The PWM feature you talk of on the 6 pins is actually implemented in hardware inside the ATMEGA328,

     

    Hardware PWM is good because it means that once the PWM is started the code need not do anything for it to continue unless you want to change its parameters or stop it all together so you have ALL the CPU power for other things

    Also the Hardware PWM will be able to go as high as 8 Mhz on a 16Mhz Arduino if you know how to setup the hardware correctly

     

    The downside of software PWM is your code has to continually update the pins involved and maintain timers for the purpose. The drawback of this is that it will not be as precise as the physical timers inside the chip and that it will take away from performing other processing in the arduino. (Less time to do other things) and if another task takes a little longer it will affect your output PWM waveform

    The upside of course is that you can use any pin as a software PWM.

     

    The reason not all pins have this is because of cost and complexity, all the overloaded pins on the arduino have to include multiplexers to route the required internal hardware to the pin, the more options the more complex and of course the more costly. It is a compromise between functionality and cost

     

    Hope this clarifies things

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  • 0

    The PWM feature you talk of on the 6 pins is actually implemented in hardware inside the ATMEGA328,

     

    Hardware PWM is good because it means that once the PWM is started the code need not do anything for it to continue unless you want to change its parameters or stop it all together so you have ALL the CPU power for other things

    Also the Hardware PWM will be able to go as high as 8 Mhz on a 16Mhz Arduino if you know how to setup the hardware correctly

     

    The downside of software PWM is your code has to continually update the pins involved and maintain timers for the purpose. The drawback of this is that it will not be as precise as the physical timers inside the chip and that it will take away from performing other processing in the arduino. (Less time to do other things) and if another task takes a little longer it will affect your output PWM waveform

    The upside of course is that you can use any pin as a software PWM.

     

    The reason not all pins have this is because of cost and complexity, all the overloaded pins on the arduino have to include multiplexers to route the required internal hardware to the pin, the more options the more complex and of course the more costly. It is a compromise between functionality and cost

     

    Hope this clarifies things

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