You should avoid interfering with the internal UART interrupt. Instead poll in main()
buf_RX[i++] = SCB_SpiUartReadRxData();
look for a delimiter in the message received as \n or \r, then process the message and reset i
arek, Attached is UART_RX project, which uses circular buffer to receive incoming strings an separate them into tokens. You can adjust Rx buffer size to your needs.