2 Replies Latest reply on Mar 21, 2016 6:52 PM by dinaline_1572371

    WDT with RTC caution!!!

    dinaline_1572371

      Thanks to Bob,

         

      I almost did implement RTC with WDT. and Now I want to know some caution about this process

         

       

         

      1. I implemented 2 years-period timer with RTC. I used WDT2 with my generated interrupt.

         

      but I worried about distortion. because of RTC, WDT2 must operate correctly. so tell me about caution that can distort WDT2.

         

       

         

      2. can you tell me about guaranteed error related to RTC? last question, you said RTC could be almost precise. but i doubt that because of

         

      clock accuracy, crystal characteristic or  load capacitance.

         

       

         

      3. and now I calculate current in circumstance that is between deep sleep and active. but in datasheet. only wake time(25us) existed.

         

      but in order to calculate exact time. I must know about code execution time, deep sleep time, active time during 1s.

         

       

         

      - sean

        • 1. Re: WDT with RTC caution!!!
          user_1377889

          Maintaining the precision of the 32kHz clock is on you allone.

             

          Precision depends on

             
                
          • Initial crystal precision
          •     
          • Temperature
          •     
          • Aging of the components
          •    
             

          All these factors are not related to the PSoC

             

          High precision clock crystals can be trimmed to 20ppm precision. Within 2 years = 2*365*24*60*60s = 63072000s you will have to expect a deviation of 63072000s*0,00002 = 1261,44s = 21minutes.

             

          When you cannot live with that you will need to correct the clock by connecting to a radio-controlled clock module. Additionally you could consider using energy harvesting (Solar, piezo)).

             

          in order to calculate exact time. I must know about code execution time, deep sleep time, active time during 1s.

             

          I would suggest you to measure your program execution times yourself.

             

           

             

          Bob

          • 2. Re: WDT with RTC caution!!!
            dinaline_1572371

            Thanks. I misunderstood sleep process will divided into some sections.

               

            and fortunately clock is only affected by ppm.

               

            Thanks for your help

               

             

               

            - sean