Hi,
As you know that the the LPC845 has SWM module(Switch Matrix Module), which enables the peripheral pin to route any port pin.
For example, if you write the code:
CLOCK_EnableClock(kCLOCK_Swm);
SWM0->PINASSIGN_DATA[0]=0x00;
SWM0->PINASSIGN_DATA[0]|=0x03|0x04<<8; //the P0_3 will function as uart_txd pin. the P0_4 will function as uart_rxd pin.

Hope it is helpful
BR
XiangJun Rong