Why FRDM-K64F UART does not work with external supply?

[francescosalvat]

Hi,

i'm developing on a project that uses a lot of UARTs on the board. When i use my PC's USB port to supply the FRDM-K64F all UARTs works fine, but when i try to supply the board using VIN pin (5V) seems that UARTs communications are loopbacked, like that RX and TX pins were shorted.

I tried also to supply the board using USB connector with an external USB charger but it did the same thing.

It works correctly only with PC's USB port connected.

Thank you!

[gerhardheinzel]

Hi everyone, is this problem solved?

I have the same problem with UART4 (PTC14,PTC15) on the K64F development board. It works ok when powered from the debugging USB connector, but does nothing at all when plugged into my main board. Oscilloscope show no activity at all. The same thing for UART3 (PTB10,PTB11) works fine independent of power or environment.

[mjbcswitzerland]

Gerhard

Problems on the FRDM-K64F often stem from the fact that there is a large capacitor on the NMI/EzPort input.

Make sure that you configure the chip to disable NMI and EzPort mode (in its Flash configuration) and then it should behave the same in all cases.

Try the link I posted a year ago (above) to check board and see this video for an overview of the Flash Configuration area:

https://www.youtube.com/watch?v=c9GRYXFs9LU

Regards

Mark

[kerryzhou]

Hi Francesco Salvatore,

    What the voltage your are powering on the K64 MCU?

   Take care, the VDD supply voltage is 1.71-3.6V.

    I think, you should check your power circuit, when your use 5V supplier, did you converter it to 3.3V? Did you measure the MCU voltage?

   Besides, use the oscilloscope test the UART TX and RX pin, whether the UART communicate wave is correct.

Wish it helps you!
If you still have question, please contact with me!

Have a great day,

Jingjing

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[mjbcswitzerland]

Hi Francesco

I don't know of any such effects in the FRDM-K64F hardware so maybe there is a SW issue when the USB is connected (?).

You can load a reference from

http://www.utasker.com/kinetis/FRDM-K64F.html

which allows you to test and verify all 5 available FRDM-K64F UARTS powering from the K64 USB interface (it will allow you to communicate with 5 independent virtual COM ports to the individual UARTs for simplicity) so that you can check the basic behavior and identify any HW issues if they were to exist.

In case of SW issues you can also use the uTasker project as fall-back in case you require a complete, immediate and guaranteed solution without any potential issues.

Regards

Mark