Lpc2000

bruce_p1 wrote:

>I was searching through this group to see if anyone else was having 
>an unreliable secondary JTAG connection issue with the LPC210x 
>chips; guess I'm not alone.
>
>I too am using a Nohau JTAG debugger; the EMUL-ARM, but that doesn't 
>seem to be the issue.
>
>According to the LPC210x datasheet, to enable secondary JTAG you 
>have to bring DBGSEL or RTCK low to disable primary JTAG pins and 
>ETM, then setup the secondary pins in software.  My original setup 
>was RTCK high and DBGSEL low.  It worked perfectly on some boards, 
>but not on my current board.  Then I tried both pins low with the 
>same results.
>
>After much searching through groups and sites, I found a note from 
>an LPC user that said he had pulled DBGSEL high and RTCK low to fix 
>random LPC210x chips that wouldn't go into secondary JTAG.
>
>This worked perfectly and I could recreate the scenario every time!
>
>I have a question into Philips as to what the real deal is and why 
>this works.  I was wondering if it was a reset or power sequencing 
>issue since I have other boards that don't do this.  Since all the 
>signals are internal to the chip, it sure seems like an issue on 
>random LPC210x chips.
>
>Regardless, I thought I'd pass this along since it seemed to be a 
>hot topic a while back.
>
>Comments or similar experiences?
>
>
>  
>
Yup, I got bit! Cost me about 4..6 hours of buzzing out the first 
prototype against the second PCB run prototypes. That was before I 
recalled this posting you made. Pull DBGSEL high, JTAG now works. Funny 
the manual says nothing about this, actually it is very misleading and 
they really really really need to work on that...

Once you've been bitten by this vague wording (Page 7 of the Rev. 05 \ufffd 
22 December 2004 LPC2106 manual): "Debug Select: When LOW, the part 
operates normally. When HIGH, debug mode is entered. Input pin with 
internal pull-down."

THEN(!) the poorly written phrase becomes crystal clear!

Lousy Tech Writers anyhow...

Regards,

TomW


-- 
Tom Walsh - WN3L - Embedded Systems Consultant
http://openhardware.net, http://cyberiansoftware.com
"Windows? No thanks, I have work to do..."
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