I installed the coin cell holder on Freedom KL46Z but still can't get system to keep time without USB connection for power

[williamstapleto]

I wanted to use the real-time clock on the freedom KL46Z.

I installed the coin cell holder and put in a CR2032.

The real-time clock program keeps time as long as the board is connected to USB but loses the time as soon as it is disconnected from USB.

The board does not seem to be getting power from the coin cell.

Any ideas?

[mjbcswitzerland]

Hi

The KL parts do not have a RTC battery domain so you need to use the coin cell to supply the processor all of the time when main power is removed. That means, you need to switch to a very low power mode rather than power down.

Also the RTC will not continue operating in this mode, it will just freeze the time, unless you supply a 32kHz clock to it (that is, use an external oscillator and not the internal one).

It is possible to use the LPO as clock source, to avoid external oscialltor, but it is not very accuarate and so is only suitable for alarm wakeups when 10% inaccuracy is still OK.

Get more info at http://www.utasker.com/kinetis/KL_RTC.html

and complete solution from http://www.utasker.com/kinetis/FRDM-KL46Z.html or http://www.utasker.com/kinetis/TWR-KL46Z48M.html (the TWR board does have a low power 32kHz oscialltor on it to allow it to work accurately).

Regards

Mark