High overshoot in UART signal

[ndc_bee]

Hi Nordic

In our product, nRF52832 is connected with another MCU through UART. We find that the overshoot in UART signal is very high.

The yellow one is the TX signal. The highest voltage is about 4V. Test point is at the pin of nRF52832.

The UART interface uses GPIO P0.05 to P0.08.

We want to ask that does this overshoot damage the nRF52832 chip?

[ketiljo]

Are you using very long wires to the oscilloscope? 

Max voltage on any pin is VDD + 0.3 V. Above this, the ESD protection diode to VDD will start to conduct. The current will increase and the voltage will be limited to this level, unless the drive strength of the other MCU is very high. So I think it's just a measuring problem.

[ndc_bee]

Thank you for your reply.

The prob I use is as follow, the GND path is not too long.

And as compare, I test the TX signal both on the nRF52832 pin side and on another MCU pin side.

Result 1 nRF52832 pin side

 Result 2 MCU pin side

The result is almost the same.

We also test the RX signal and find that the signal is much better.

Result 3 RX signal on the MCU side

The TX signal layout and the RX signal layout is almost the same. So we think that the TX signal from the MCU side may be a little problem. We are going to adjust the register of the GPIO in the next step.