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Strange UART TX Signal on LPC 54628 (OM13098)

Question asked by arecz on Mar 19, 2019
Latest reply on Apr 1, 2019 by Kerry Zhou

Hi all.

I'm using OM13098 board with LPC 54628. First, I used the UART drivers demo from SDK_2.4.1_LPCXpresso54628 which uses UART0 through USB debug link VCOM.


After I adapted the basic Uart Polling echo demo to use UART4 (FlexComm4) from J13 pin 13/15 (TX/RX) [lpc pin 3_26/ pin3_27]. No problem for the UART to receive data from a USB-RS232_0V converter and using TeraTerm. But here i'm facing a issue for the TX. Every data is not well displayed by TeraTerm, so I decided modify code to send only character "a" and check signal on J13 pin 15.


In picture in attachment, signal is +/-250mV ?! I don't unsterdand why. It should be between 0V and +5V. Code in attachment


Thanks for any help,