It's not clear what you're asking. Can you provide the exact problem/analysis you've been asked to do? You need to measure the voltage (and presumably current) for the LPC supply? It can run over a range of voltages, so you would have to define what supply voltage is to be used. Current consumption varies with clock frequency, which peripherals are used, what's connected to the pins, if sleep mode is used, etc. If you really need to measure micro impedance you would have to specify which pin you are talking about and what mode the pin is in and which peripheral is connected to that pin. Sometimes you do care about pin impedance - say if it's an ADC pin or even just a Digital Pin with internal pullup.

So the aim of my project is to measure the characteristics of power from the mains supply. So in order for it to be fed into the micrcontroller I have reduced the 230V AC to 5V AC. However, I was told the internal impedance should be somewhere in the region of MOhms so the voltage going into the LPC1768 is still the 5V (as with a smaller internal impedance there would be current and so the Voltage would be different thus not giving an accurate reading). But I can't find the internal impedance anywhere so I was told to measure the voltage at the LPC1768 using a voltmeter, I was just wondering if there was any way of doing this? Thanks for the reply!