FRDM-KL46Z RTC runs only with powered USB OpenSDA cable

[york9]

I use mbed to write the application on to the board FRDM-KL46Z.

The board is powered with Vin 5-9V.

Application runs, but reading the time with

time_t seconds = time(NULL);

will get the same result until the board is powered

with the USB cable at the OpenSDA port in addition.

Is there a chance to power up the board without

the USB cable to keep RTC running?

Thank you.

[daweiyou]

PLS see KL46 RTC_CLKIN pin, which provide RTC clock src for RTC module, so if you have separate power for FRDM board, PLS provide such clock from J16 Pin12.

Or MCU generate such clock by itself;

Opensda interface: K20 generate such clock after powered from USB cable.

Dawei You（尤大为）

[mjbcswitzerland]

Hi

The mbed OpenSDA (present version 20140530_k20dx128_kl46z_if_opensda.s19) generates a 32.768kHz clock on the PTC1 (RTC_CLKIN) which can be used as RTC clock (when the debugger interface is powered). However many users will have programmed the P&E version (eg. MSD-DEBUG-FRDM-KL46Z48M_Pemicro_v114.SDA) so that it works with CodeWarrior or KDS (the mbed version doesn't work with these IDEs) and so the signal is not present. The fact that this clock is present is not specified in the FRDM-KL46Z user's manual - possibly due to the fact that the P&E version is expected - possibly also because it seems to be little-known fact which is possibly not officially stated anywhere (good idea by the developer though - perhaps P&E could do the same?)

Comparing with the TWR-KL46Z it is seen that a low power clock generator is connected to RTC_CLKIN so that the clock signal is always available, which is the method that will presumably be used in most cases.

If the accuracy of the RTC is not critical and one would like to operate the FRDM-KL46Z RTC (maybe just for test purposes) without an external clock it can also be clocked from the internal 1kHz low power clock, which avoids needing the external clock input and also makes use independent of the debug software that is loaded/used.

Regards

Mark

[york9]

Thank you for the good explanation.

In my case the board is powered with 5V external at P5-9V VIN

and an injection of 5V at pin 1 of J16 will work for me,

without powering it with a OpenSDA USB cable.