Lpc2000

Landrum Haddix wrote:

>Hi,
>
>I found a really hard to track down hardware problem today
>that was forcing the JTAG port to not work.
>
>I am using an LCP2138 and JTAG quit working after a board rev.
>
>  
>
You probably are looking at an early release of the LPC213x manual?  The 
"Rev 01 - 24 June 2005" issue of "LPC213x User Manual" clearly documents 
that P0.31 must not be pulled low during reset...

I do know that the manual prior to that revision date was rather terse 
(missing data).

TomW



>We had pulled P0.31 down because it was the enable for a 485
>transciever and needed to be low during reset.
>
>Turns out there is an 'undocumented feature' on some of the LPC
>parts including the 2138 that will disable JTAG if P0.31 is low during
>reset. We all know about RTCLK needing to be high during reset
>for JTAG because it's documented, but P0.31 functions exactly the
>same way.
>
>I think it all has to do with a obscure thing called the secondary JTAG
>port.  I think for some of the series P0.31 functions like RTCLK on the
>2138 and must be low at reset to enable the JTAG port.
>Apperently it's still in the silicon even on the 2138 even though it's
>not documented.
>
>Anyhow it was very obscure and if it weren't for a single message 
>buried deeply on the Keil site I would not have found until I removed 
>every change on the new rev.
>
>
>Landrum Haddix
>lhaddix@...
>http://web.qx.net/lhaddix
>
>
>
>
> 
>Yahoo! Groups Links
>
>
>
> 
>
>
>  
>


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