[NBLUG/talk] JTAG Anyone?

Bob Blick bob at ted.net
Fri Feb 16 11:13:18 PST 2007


Hi Robert,

Most JTAG interfaces are standard. Yours is. You can get cheap ones at 
SparkFun Electronics that connect to the printer port:
http://www.sparkfun.com

Look at ARM or MSP dev tools. Either of those will work, ignore the extra 
non-JTAG-specific pins, they are used for debugging and are specifif to 
those processors. You'll spend about $20.

The only thing that really changes much is the connector. But as long as 
you connect the right pins it all works. And it doesn't hurt things unless 
you get it really wrong.

Back in the 5 volt days you could just connect three resistors to the 
printer port and do JTAG but now that everything's 3.3 volts you do need 
some level shifting.

The USB JTAG interfaces usually just add a USB-to-printer-port chip, so if 
you have a printer port already it's actually better.

If you want to build one yourself(not recommended because $20 is a good 
deal, but you might like to have the info so you can see how generic it 
actually is) you can Google "build JTAG wiggler". Also look at:
http://hri.sourceforge.net/tools/jtag_faq_org.html

Cheerful regards,

Bob


> I'm interested in getting into JTAG so I can get an embedded board (Ceiva 2 - 
> http://www.rangat.org/rthille/Computer/Ceiva2/ ) that I'm interested in 
> getting Linux or NetBSD running on.  The trouble is, I can't figure out a way 
> to break into any sort of bootloader over the serial port it's got.  So I 
> need JTAG to flash it with a bootloader.
>
> I've looked around and it looks like there are two approaches to JTAG, 
> parallel (cheap) and USB (mostly expensive or very expensive).  I did find a 
> pretty cheap USB->JTAG adapter which is supposed to work with the GNU 
> toolchain. http://www.amontec.com/jtagkey-tiny.shtml  One possible problem is 
> they only seem to only support ARM & Xscale procs at this time on the 
> jtagkey-tiny.
>
> It's 29 Euro, but since it's coming from Switzerland, the shipping is another 
> 27.1 Euro.  So, I'm interested in finding out if anyone else wants one and we 
> can split the shipping.  I'll front the money, take the risk, etc...
>
> Let me know if you're interested, even if you'd be interested in one of their 
> other products that supports MIPS.



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