High overshoot in UART signal

RE: High overshoot in UART signal

user65515 — Wed, 25 May 2022 15:23:58 GMT

Looks like you are using x1 probe setting; try instead using x10 setting (10MOhm impedance). The traces still don't look correctly matched to the instrument - they should be perfectly flat outside the transitions.

RE: High overshoot in UART signal

user82895 — Wed, 25 May 2022 00:46:42 GMT

Thank you for your answer.

We have calibrate the prob before the test and use a short GND path.

So I think this may not be the main reason for this situation.

RE: High overshoot in UART signal

user82895 — Wed, 25 May 2022 00:44:01 GMT

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.

RE: High overshoot in UART signal

user65515 — Tue, 24 May 2022 19:29:24 GMT

The probe is unbalanced (not correctly compensated to match the instrument); look for the tiny screw adjuster on the probe and slightly rotate with a screwdriver to bring the trace flat rather than curved which will also reduce the displayed (apparent) overshoot. Also ensure the 'scope probe Gnd connection to 0V is used for cleanest display.

RE: High overshoot in UART signal

ketiljo — Tue, 24 May 2022 12:42:00 GMT

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.