Lpc2000

--- In lpc2000@yahoogroups.com, "onceinfour" <mmack287@h...> wrote:
> I am thinking of using an LPC22xx as a single chip micro in an 
> industrial controller board.  2 questions.  I assume the device can 
> be used to count external pulses, encoder signal, which pin(s) can
be 
> used for a counter i/p?  
> The LPC2xxx's supposedly have a built in RTC?  Anyone got any info
on 
> connecting a battery or super cap to maintain the RTC contents
during 
> power down?

I took a look at the specs concerning this and I don't think it will
be overly practical.  The max current drain with *nothing* running
over temp is 0.5 mA.  Unless you are using a rechargable battery and
power will be supplied every day or at least week, this is rather
high.  The RTC in the LPC2x is not really setup for battery operation
since you have to power the whole chip to keep the clock going.  

There are two ways to deal with this.  

1) Use and external RTC.  These are not overly expensive.  Since you
need a power on reset, you can combine these two in one chip using
something like the SH3000 uBuddy from Semtech.  It can cut the clock
to the ARM and handles the whole POR/BOD issue as well as providing an
RTC and generates a high speed clock from the 32kH xtal.  Pretty cool
for a lot of apps where the CPU needs external devices like this. 

2) Use an ARM that provides a *real* battery backed RTC like the
AT91M55800A.  This guy has a separate RTC with a battery power input
and runs on 1-2 uA of current when the power is off.  It has a control
input and an output to let the RTC wake up the CPU and cut power when
it is not running.  Also pretty cool.  :)