Lpc2000

Ranjith,

>  For Power Mangement, Other than the Software What are the Cares should be
> taken in Hardware for LPC2138?
>  (Like Pull-up resistor..etc)

it's all about reading datasheets ...

Vih = 2.0V, Iih = 3 uA. For pins that carry internal pull up/downs Ipd =
150 uA and Ipu = -85 uA.
Check the datasheet/use manual for which pins have internal pulls.

Values of pull-up/down resistors are not critical. If you use the IO pin
that has to have a pull-up as output (or even input) pin bear in mind that
a current will flow (my board has 3 kOhm pull-ups so that about 1 mA).
This is depending on your application and schematics.

Don't use the option of removing power from the processor, this will make
all IO pins floating (if no external pull-up/down resistors are used)
unless you really know what you are up to (but then, would you still be
asking this question ???).
If you do use this (or if you apply an external reset) make sure the pins
for selecting bootrom, debug and trace (see user manual) have to
appropriate values.

I think this is fairly obvious and I have done similar things in previous
projects with battery/power management.

One thing to watch for is the Real Time Clock. The RTC can be driven
either by the Peripheral clock or a 32 kHz crystal. The Peripheral clock
stops when you put the lpc21xx in power down mode. So if you rely on the
RTC, make sure you use the 32 kHz oscillator (not available in lpc2104/5/6
...)

Good luck,

    Rob