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Newbie Question about Status and Control Registers on Uno

grovesr

Hi,

I am somewhat new to microcontrollers and am just getting to the point where I am starting to mess around with the timer registers.  I have learned how to use the CTC features to generate divided clock outputs.  In doing this I discovered that the changes that I made to the timer control registers seem to be persistent, when I load in a new program using the Arduino IDE.  I had assumed that whenever I loaded in a new program, the control registers would be reset to some default initial state (i.e. all "0").  Am I correct that the timer control registers do not get reset when loading in a new program?

 

I am currently forcing the timer control registers back to an initial "0" state at the top of my program before I start setting the bits I want to play around with.  I am mainly asking because I have never seen any other code example where the control registers get reset to "0" at the beginning, and I am wondering if I am perhaps doing something wrong.

 

Thanks.

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    Hi Robert,

     

    I am not fully conversant in Arduino code, but in general an MCU will have some default state for all registers.  Usually they are set to a state where no bad things happen when the MCU powers up and begins loading the boot code.  So if you have code or definitions that setup the control registers, then that is what you will see when you turn it on.

     

    Usually a control register is write only, though I have seen MCU's where you could indeed read the current control states.  If you want to test this feature, set up a loop where you cycle each bit in the register on and off.  Set up your debug to monitor the registers and see what happens.

     

    Hopefully someone who knows the Arduino better than I can tell you for sure.

     

    DAB

  • 0 in reply to DAB

    Thanks for the response DAB.

     

    I guess I'm most interested in what happens on uploading my program to the Arduino.  Do the registers all get defaulted to some initial state, then my code is loaded and run, setting the new register bits as I desire?  Or do the registers retain their previous values and any bit-by-bit setting of registers done in  my code are additive to the previously saved state?  My understanding is that the control registers map to locations in the Flash memory, so I think they should retain their information.

     

    It's just a question of what is the initial state of the registers immediately after uploading my code, and before actually running my code?

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  • 0 in reply to DAB

    Thanks for the response DAB.

     

    I guess I'm most interested in what happens on uploading my program to the Arduino.  Do the registers all get defaulted to some initial state, then my code is loaded and run, setting the new register bits as I desire?  Or do the registers retain their previous values and any bit-by-bit setting of registers done in  my code are additive to the previously saved state?  My understanding is that the control registers map to locations in the Flash memory, so I think they should retain their information.

     

    It's just a question of what is the initial state of the registers immediately after uploading my code, and before actually running my code?

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