KL03 with external MHz clock

[martinkrause]

Hi, we are running a custom board with KL03Z32 mcu. The mcu is running at 8 MHz from LIRC. We use the LPUART to communicate to another board. The LPUART is clocked from LIRC. Unfortunately the LIRC only has an accuracy of +/- 3%. This is not enough to meet the baud rate requirements. Using the more precise 48 MHz HIRC (with +/- 1% accuracy) is not an option, because the power consumption then will be too high (according to the data sheet). So our idea was to use an external crystal oscillator with a high accuracy (+/- 20 ppm). But if I understand the data sheet/user manual, then the allowed range for the external clock is 32 kHz ... 40 kHz and the mcu has no internall PLL to increase this freqency internally. So it seems not to be possible tu run the CPU with 8 MHz with an external (high accuracy) clock. Is this correct? Is there any chance to achieve a baud rate accuracy better than +/- 3% when running from LIRC?

Best regards,

Martin

[martinkrause]

Hi Stano,

ah! In the data sheet of the KL03 we read that "Oscillator crystal or resonator frequency" is between 32 kHz and 40 kHz. So if we use an external crystal it has to met this reqirements, but if we use an exteranl clock generated by - for example an oscillator - higher frequencies are allowed?

You wrote an external frequency up to 48 MHz is allowed. In the data sheet there is fERCLK (External reference clock) specified as <= 16 MHz. What is correct, 16 MHz or 48 MHz. Or does fERCLK mean something different?

Best Regards,

Martin

[Stano]

Hi Martin,

you are right, for the VLPR and VLPS mode it is 16MHz, but for normal run mode it can be up to 48MHz.

In case you want to use VLPR mode, thus 16MHz is the limit.

Best Regards,

Stano.

[Stano]

Hi Martin,

it is possible to use the external oscillator as the clock source for MCU with frequency up to 48MHz also. The external clock source has to be connected to EXTAL pin and set the MCG_C1_CLKS = 10. Then the external clock source is used as the main clock source for MCU. Then it is possible the use internal dividers OUTDIV1 and OUTDIV4 to set the required frequency for all internal peripherals.

I think it helps you to solve your issue.

Best Regards,

Stano.