Lpc2000

James
  I have an LPC board running with a 14.7456MHz crystal and it is
solid for both JTAG and Download.  However, even though the crystal
is parallel resonant w/ 18pf load, the circuit has 39pfd on both
sides of the crystal - not sure where we got that piece of info.
Anyway, it's something you might try.

-Bill



On Fri, 7 May 2004 12:37:02 -0400, James Dabbs 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.

-James





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