5 Replies Latest reply on Aug 4, 2011 12:30 AM by udayanu_

    RTC with external non-crystal clock




      Since there is no clock input on the the RTC component, can I possibly use a 1pps input on a digital pin as the source for the RTC interrupt?


      Somehow I clicked on the RTC ISR in the Interrupts tab of the design wide resources and it brought up RTC_v1_6.cysch. If I modify this, will I break all further RTC designs (since it seems to be in the component library)


      Alternately, is there a way of providing an external 32.768 kHz external clock this resource can use?



        • 1. Re: RTC with external non-crystal clock
          • It is possible to use an external 1PPS signal to drive the RTC, please see this thread for the implementation, http://secure.cypress.com/?app=forum&id=2233&rID=51134 .
          • Modifying the component in a project is local to your project. It will not affect the actual RTC component. The component can be reused in its original form in other projects.

          I hope this helps.

          • 2. Re: RTC with external non-crystal clock

            Hi Willemite,




            The 32.768 KHz external crystal oscillator can be used by checking the "XTAL32kHz" tab in the "Configure System Clocks" dialog box which is found in the "Clocks" tab of .cydwr file.

            • 3. Re: RTC with external non-crystal clock

              Thanks for the suggestions, I forgot to mention I cannot use the XTAL 32 pins because I have the first touch kit, which has these reserved pins mapped to the pushbutton switch and one of the accelerometer control pins. 


              If I do not have the 32kHz watch crystal enabled I get this error:
              "The 32KHz watch crystal is not enabled and must be active for the one pulse per second interrupt to function.

              The one pulse per second interrupt from the PM system requires the 32KHz crystal to be enabled. Review and update the 32KHz clock your design and rebuild."



              If I enable it, its also not happy:


              "Pin Error: (Invalid pin assignment. This pin has been reserved for use by the 'XTAL 32kHz' clock.).

              A pin assignment is currently in an error state."


              I tried adding the generated RTC source (from a different workspace) to the project directly, but then it would not compile as it could not find "cyPm.h: No such file or directory "

              • 4. Re: RTC with external non-crystal clock

                Hi Willemite,




                Using RTC component with External 32.768kHz crystal would be difficult on First Touch Kit if you are planning to use even the Accelerometer present on the board.


                For this purpose, one solution would be to use the APIs generated from an RTC component into the the project without actually using an RTC component.




                In such a case, external 1PPS signal is required for the RTC functionality to be implemented.