Lpc2000

--- In lpc2000@yahoogroups.com, "beano040461" <paulbearne@b...> wrote:
> 
> --- In lpc2000@yahoogroups.com, "wittrockjeff" <jwittrock@m...> 
wrote:
> > 
> > Hello All,
> > 
> > I have not used any of the LPCxxx devices before.  I am 
considering 
> > using an LPC2138 in an application which must read data from an 
> > ADS1271 24bit A/D using an SPI interface.
> > 
> > In looking at the SSP specification for the LPC2138, it can 
handle a 
> > maximum frame size of 16 bits.  Does anyone know of a way to 
extend 
> > this to 24bits without CPU intervention? Has anyone done 
something 
> > similar?  The ADS2171 will have a 100kHz data rate, so I'm 
worried 
> > about having interrupts on a Byte by Byte basis, as that would be 
a 
> > 300kHz interrupt rate (100kHz X 24/8).
> > 
> > Thanks for any help.
> > Jeff
> > 
> > p.s. Great user group.  Lots of good info.
> 
> Hi Jeff
> we are using 2138 with and ads1251 but only at 9.6Khz the problem we
> had running at faster rates is processing the data at the current 
rate
> we only have 104us to work with between measurements at 100Khz this 
is
> down to 10us not sure about the 1271 but the 1251 requires some 
block
> averaging of readings to achieve the the maximum resolution is this 
case?
> 
> paul


Hello Paul,

You are right about having to do filtering in software in order to 
use the high resolution to best advantage.

I don't expect to be able to do much (any?) signal processing in real 
time.  Instead I would just shoot the A/D results into a reasonable 
size buffer, and do AVG or RMS calculations after the fact.

One other requirement for this project would require some real time 
math.  I would be integrating a voltage from a flux sense coil.  This 
requires a continuous conversion and adding the A/D result to what 
would probably have to be a floating point variable.

This is my first look at any ARM core, so I'm still looking at things 
like interrupt response time, speed of floating point math with GNU 
tools, or IAR tools etc, and am unsure if its a very good fit for 
what I'm trying to do. 

Thanks,
WITTROCK