Lpc2000

--- In lpc2000@yahoogroups.com, "vrrraju" <vrrraju@y...> wrote:
> Dear Friends,
> 
> I am trying to make an evaluation board for myself and later for 
> commercial purpose based on LPC2106. I have little doubts on reset 
> circuitry. I am planning to use a RC circuit of 10K and 100nF to 
> reduce the cost. Otherwise is it compulsory to use Reset IC for this 
> purpose. Please suggest me on this circuit.
> 
> Thanks in advance.

This is a tricky circuit depending on how well you want it to work. 
Most modern MCUs have a POR (power on reset) and BOD (brown out
detect) built in.  I am surprised that the LPC parts don't.  

If you are just doing a hobbiest design, an RC will work ok.  But if
you plan to sell this board commercially, you will want to use a POR
chip.  The problem with an RC circuit is that although it works great
for power up, it does not work for power down or for any short
duration or brown out power conditions.  If the voltage drop is
shorter than your RC time, the chip will not be reset, but can be
upset.  If the voltage does not go to ground, same thing.  

If you are adding your own power regulators, you can often find units
that have a power ok output.  These can normally be wire OR'd together
to control the reset.  Some even provide a timeout period.  

If you want reliable reset operation, use an external chip.  And
complain to Philips.  There is no reason that they could not have
added POR and BOD to their devices.