I am using LPC2148 MCB2140 board. How to measure current consumption of LPC2148 in power down mode? On which pins should I keep the multimeter to measure the current?
You should obviously have the multimeter measure the current out of the power supply.
Because your circuit will consume current from all the VDD to VCC pins of the chip.
But your circuit will also consume current for I/O pins, pull-ups, pull-downs, LEDs etc.
If you measure on the power supply, you can see how much the current consumption changes when the processor enters power-save, and what happens when you put individual I/O pins high, low, or tristated.