Lpc2000

Hello,   
   
in my application I sporadically get UNDEFINED exceptions, though   
running from internal flash (LPC2138).   
   
Is there any public (assembler) source code available to analyze the   
stack for the location of the particular instruction causing the   
exception?  
   
Any general hints about the cause of such an exception, except the   
PC somehow gone to the woods, are appreciated...  
  
Gunter