Content originally posted in LPCWare by Rob65 on Wed Nov 20 23:43:52 MST 2013
Check the user manual again and start from the beginning of the UART chapter.
There you will find a step by step instruction of what to do: enable the UART, select the IP clock to use, set the pins to the correct functions, setup uart.
You need to have your UART pins setup properly through the PINSEL registers. That connects the UART lines to the selected pins.
As LabRat already pointed out: the examples that come with the LPCXpresso tools should be working straight out of the box.
Of course you need to use the hardware as used with the examples.
What hardware do you have, did you use a scope (or any other means) to verify if there is data coming from your TX pin, did you try to debug your program - what happened.
You need to figure out how your hardware works and how you initialize the peripherals - this is similar for all peripherals in the chip so try to get the hang of this other wise you'll be stuck forever.
Rob