LPUART1 RX signal of S32K148 is distorted.

[toipaz]

I'm using S32K148-EVB (nxp.s32k148evb-q176).
I am testing the example to use uart, but the rx signal from lpuart1 is strange.

* Connection:
 PC -- USB to serial ------------ RS-232 Converter ---------- EVB

- Pin LPUART1 RX, PTC6

- Pin LPUART1 TX, PTC7

Test code: lpuart_echo_s32k148 example of S32K1xx SDK RTM v4.0.3
There are no modifications to the example code.

1) EVB --> Transfer to PC: OK (attached)

result screen in PC 

2) PC --> EVB transfer: nothing

When checking the signal using scope, If it is connected to the EVB's LPUART RX line, the RX signal will be distorted.

Scope image:
* RS-232 Converter output signal (red) with EVB’s LPUART RX Line connected:

Signal when RX Line is connected. 

* RS-232 Converter output signal (red) without connection:

Signal without connection of EVB RX line 

I still used it without any modifications to the example code.
Is there a solution?

[Robin_Shen]

Hi

Maybe I didn't understand your question.
But shouldn't a USB to TTL Converter be used to connect the PC and EVB?
If you use a USB to RS232 Converter, the RS232 signal voltage cannot be directly connected to the 5v or 3.3v signal on the EVB board.

Best Regards,
Robin
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[toipaz]

Thanks for your reply.

I wrote it wrong in my question. Let me correct as follows.:
The connection is
     PC [USB]--- USB to RS-232 converter -------RS 232 to TTL --- EVB
The power source for RS-232 to TTL uses 5V DC from EVB.

The RS232 to TTL converter is equivalent to the Arduino RS232 shield.

Best regards.

[Robin_Shen · Accepted solution]

The PTC6 is connect to OpenSDA(K20) by default, maybe it was caused by it.
Have you try to power the S32K148EVB by external 12v(J9) instead of USB power(J24)? Or change the hardware by remove R627.

[toipaz]

Thank you for answer.

It is currently connected via external 12V DC, and USB is connected at the same time.

As mentioned, when I tried to communicate after removing the USB,
I have confirmed that communication is working normally.

Thanks Robin.

Best Regards,

Cheolhyeon Cho

[toipaz]

Using the same example code, I changed it to test as follows:
1. lpuart1 with PTA18, PTA19 pins
2. lpuart2 with PTA8, PTA9 pins.
In both cases, 2-way communication works well.

Should I consider the PTC6 pin of my EVB board to be the problem?