Lpc2000

--- In lpc2000@yahoogroups.com, "James Dabbs" <jdabbs@t...> wrote:
> > Another question.  If the LPC is being driven by an oscillator, 
has 
> > the output of the osc been divided down and capacitively coupled 
to 
> > the LPC?  Direct drive from an external osc will allow the LPC to 
> > 'almost' work but because the waveform is distorted, the problem 
will 
> > show up when trying to download to flash.
> 
> Bill,
> 
> In this case, it's a quartz crystal, connected directly to the 
processor
> pins, coupled to ground with 18pF caps.  I should note that we 
started
> off with a 19.6608MHz crystal, and could not get the boot loader to 
do
> much more than echo back the '?' and then go into a very strange 
state.
> Dropping the freq got it working in 'hyperterm' mode, but not with 
the
> ISP loader.  We've already changed parts once, and the layout is
> bypassed very well, with the regulator at the LPC and 10uF and .1uF 
chip
> caps right up on the 3.3V and 1.8V supply pins.  Nevertheless, 
supply
> noise is still something we're thinking about.


The oscillator requires quite large value capacitors - try 33 pF.

Leon