1 Reply Latest reply on Oct 15, 2020 7:09 PM by LePo_1062026

    Is it possible to have a small part of hardware running in sleep mode? That is, is there a clock running while the processor is in sleep mode?

    DaSl_2925376

      My recent PSoc5 design spends most of its time asleep waking up by the 4o96 ms sleep timer looking to see whether it's time to do something or go back to sleep. So it could be awake for a few seconds occassionally throughout the day.

       

      However, I need to add a heartbeat flashing led.  Is there a clock I can use which does not go to sleep?

       

      The design was developed on the CY8CKIT-059 prototyping kit and the target board uses the same PSoc device

       

       

      Dafydd

        • 1. Re: Is it possible to have a small part of hardware running in sleep mode? That is, is there a clock running while the processor is in sleep mode?
          LePo_1062026

          Dafydd,

           

          By design intent, the high speed clocks (IMO, ECO, PLL, USB_CLK, MASTER_CLK and BUS_CLK and all derived clocks) are turned off to save significant current.  The rule of thumb is that a running clock consumes about 100uA/MHz.

           

          However, the ILO or the WCO can be left on in most low power modes.

           

          If you don't need timing precision, you can use ILO @ 1KHz +100%/50%.  It provide the LOWEST sleep current because the oscillation is at 1KHz.

           

          If you need more precision you can use the WCO with the accuracy of the watch crystal you can solder on to P15[3] and P15[2].  Note: The CY8CKIT-059 has 12pF caps already populated on P15[3] and P15[2].  Just solder a 32.768KHz watch crystal across these terminals on the header.   This is the second lowest sleep current since it oscillates at 32.768KHz.

           

          Watch crystals can be found in very small SMD format and can be sub-$1 in small quantities.  I use this option ALL the time.

           

          Len

           

          PS:  Using a low-cost watch crystal can also have additional benefits.   For example, I use my WCO to retrim my IMO to make the IMO frequency MUCH closer to the target frequency than the PSoC's listed accuracy.   For example, the IMO @ 3MHz is listed at +/-1%.   I have gotten better than 0.04% when I use the 100PPM watch crystal as the reference for the IMO.

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