Content originally posted in LPCWare by Polux rsv on Fri Jan 13 04:07:37 MST 2012
In the UM, chapter 8, check the PINSEL and PINMODE registers. The values at reset are explainend and you could check if the configuration is ok for your application.
In the microcontroller world, usualy, an I/O is set as an input, sometimes with a pull-up activated. But check everything, as some dedicated pins are input only, or output only.
Angelo