https://devzone.nordicsemi.com/f/nordic-q-a/36379/the-problem-of-uartI download the SDK at https://www.nordicsemi.com/eng/nordic/Products/nRF5-SDK/nRF5-SDK-zip/59011 . When I used &quot;nRF5_SDK_15.0.0_a53641a\examples\ble_central\ble_app_uart_c &quot; , it run ok. But when I changed the define of RX_PIN_NUMBER at pca10040.h . Theen-USTelligent Community 13Mon, 16 Jul 2018 16:51:07 GMThttps://devzone.nordicsemi.com/thread/140270?ContentTypeID=1Mon, 16 Jul 2018 16:51:07 GMT137ad170-7792-4731-bb38-c0d22fbe4515:0d260ae8-8c8c-409e-95b3-f5dc685ceb8aMartinBL<p>Why do you change the RX pin? Do you connect it to something else? If you connect it to something else, do you also connect the other device to ground?</p> <p>If you just change the pin number, but don&#39;t connect anything to it, it will be left floating in the wind and will pick up noise. The UART will then believe that the noise is actual data, but not be able to make sense of it. Then it generates a Communication error.&nbsp;</p><div style="clear:both;"></div>