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,