How can I use MKW01-MRB's UART via TWR-RF's on-board USB2SER?

[jongsoojeong]

Hi,

I want to direct MKW01-MRB's UART to TWR-RF's on-board USB2SER.

So I set jumper pins of J17 (MRB) like below:

2-3, 5-6, 8-9, 11-12, 14-15

But the terminal program is not showing anything. I checked MKW01-MRB's UART works without TWR-RF.

Please, help me!

-Jongsoo

[AngelC]

Dear Jongsoo,

The MRB-KW01 Development Platform Quick start Guide contains an appendix about board’s jumper settings when using it standalone or mounted in a TWR-RF-MRB board. Please make sure to follow the instructions listed in the document. You should not have any problems.

MRB-KW01 QSG: http://cache.freescale.com/files/microcontrollers/doc/user_guide/MKW01DEVPLATQSG.pdf

Regards,

AngelC

[jongsoojeong]

Thank you.

I found that using TWR-RF's USB2SER is impossible when I leave J8's 1-2 pins (MRB-side) to be opened.

To use accurate asynchronous time source, I have to wire J8's 2-3 pins for 32,768 Hz external crystal.

Is there any way to use TWR-RF's USB2SER with 32,768 Hz external crystal on MRB?

Thanks.

Jongsoo

[AngelC]

Dear Jongsoo,

The demo applications are currently configured to use the CLKOUT as source for PLL. In case you would like to use the 32.768 KHz clock as source, you may need to modify the code (MCG setup configuration and UART baud rate calculations) and use FLL instead of PLL.

There are some code references of how to achieve this in KL2x devices, which are similar to KW01. I would recommend you to have a look at the low power demo code example included in “KL25_SC” package. 

Link: http://www.freescale.com/webapp/sps/site/prod_summary.jsp?code=TWR-KL25Z48M&fpsp=1&tab=Design_Tools_...

Another approach would be to simply use the internal clock as source (Fast IRC of 4 MHz) and use practically the same code as current applications. Only the PRDIV or VDIV would need to be adjusted to match the current values. If you are using Radio Utility code, you might see it uses a CLKIN of 2Mhz . You could, for instance, modify PRDIV to be 2 (currently is 1) and therefore get the 48MHz.

Regards,

AngelC

[jongsoojeong]

Thank you, AngelC.

Without TWR-RF, I already implemented code to use FLL. And it seems correctly work on standalone MRB board.

My question is why TWR-RF's USB2SER doesn't work even with jumper settings and code to use 32768 Hz external crystal on MRB.

May there any side effects to TWR-RF by using the crystal?

Thanks,

Jongsoo

[AngelC]

Dear Jongsoo,

From the hardware side, there is not any reason why the USB2SER in TWR RF should not work with 32.768KHz crystal in MKW01-MRB. The USB2SER uses its own 4MHz clock source, so the only potential reason would me a mismatch of baud rate frequencies.

I would recommend you to verify the baud rate matches and the signal is accurate enough. Checking it with an oscilloscope probe would help.

Regards,

AngelC

[billpoole · Accepted solution]

Perhaps the XTAL_32K pin (PTA19 on MKW01) is loaded or pulled high by LED1_ Onboard on TWR to which is it connected via the jumper on J6 pin 25-26.

pull that jumper (4th from the top in your photo) and retry it.

I am concerned that there would be several cm of path length from MKW01 pin thru J14 on MRB to TWR J5 to J6 etc... picking up noise. Removing the 0 ohm R10 from the MRB would disconnect that path length.

If PTA19 is programmed to drive that LED. After you convert the oscillator on the MKW01 to use both PTA18 and PTA19 and disconnect the connection the LED will no longer be available.

Likewise the EXTAL_32K signal has a longer trace to TWR-J1-17, removing R11 on MRB disconnects that path.

Bill Poole

Freescale Applications Engineering.

[jongsoojeong]

Hi all,

I removed jumper pins for 25~27, 31~33 at J6 on TWR-RF.

It works.

Thank you.

-Jongsoo