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How to turn off / disable the internal RTC if MCU is connected to external battery?

Question asked by M I on Apr 3, 2019
Latest reply on Apr 11, 2019 by M I



I'll be developing a new product using the MKL28Z512VLL7 MCU.


I have browsed through MKL28ZRM.pdf but I don't see > a way in firmware how I can turn off / disable the internal RTC of an MCU that is connected to external battery, when the whole system is powered off / unplugged from A/C outlet?


The situation is this: after manufacturing & testing, the coin cell battery will be kept on the board without a removable disconnecting tab or tape, when storing the product on the shelf. We cannot have a removable battery tab or tape to disconnect the battery because the customer will NOT have access to the board inside the product. The internal RTC will use up the battery if it remains ticking when everything else is powered off.


I know when & how to detect when I need to turn the RTC off (after manufacturing test) & when & how to detect when I should enable it & let it start normal RTC operation.  But can it be disabled or turned off & remain off in firmware (which MCU register, port, bit setting) before full system shutdown even if there's coin battery connected to the MCU?

Is there a way I can execute in FW the disabling of the   internal RTC module (which MCU register, port, bit setting) before the whole system is powered-off through any of MKL28's registers or ports?


I need to do this in order to conserve battery life considering we can't know when the product will be bought & used by a customer.


Thanks for the help.