Lpc2000

I had a board with JTAG problems.  Started 1 in 10 or so.  Good enough
to make me think it was in the startup code somewhere.  I pulled hair -
looking at startup, swapping JTAG debuggers, etc.  

 

I finally traced this to a missing bulk bypass cap in the V1.8 supply.
The supply had high frequency oscillations on it.  Adding a cap made it
super reliable.

 

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From: lpc2000@yahoogroups.com [mailto:lpc2000@yahoogroups.com] On Behalf
Of drb5599
Sent: Wednesday, July 20, 2005 6:48 AM
To: lpc2000@yahoogroups.com
Subject: [lpc2000] LPC2131 SPI output drive and ULINK JTAG issues

 

Hello All,
After several months of developing with the MCB2130 eval board I 
finally got my first prototype hardware.  I am pretty excited, but I 
have a couple issues.  

My first big issue is the SPI output signals.  I am communicating 
with two other devices over an SPI bus where the LPC is the master.  
The signals coming out of the LPC are correct, except the peak 
voltage of the MCLK and MOSI are about 1Volt! 
Orignally, I had buffers on all the SPI lines, but due to cost 
pressure I had to take them out. I read that the max output current 
for the LPC pins is like 4mA.

Question:  Are the LPC2131 outputs really that wimpy?  Has anybody 
else had this problem?  Did you just add buffers?

Second issue is with the JTAG interface.
The ULINK worked flawless with the MCB2130 eval board running with 
12MHz crystal.  But my hardware uses a 12.288MHz crystal.  I have 
changed the crystal and PLL settings in startup.s and the debugger 
but, I is still very unreliable.  I have gotten it to work about 3 
times out of 50?  Mostly, I download my code using the Philips Flash 
Utility over the serial port.

Also, I worked thru all the suggestions in the Keil knowledgebase 
regarding "JTAG Communication Failure" with the ULINK.  None of 
these things fixed it.  I suspect it has something to do with the 
clock settings.
Does anybody know of any other tricks or secret clock settings in 
uVision3 or startup.s?

Thanks,
Dave Butler





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