AVR-Chat

> From: ecros_technology
> 
> --- In AVR-Chat@yahoogroups.com, "Chuck Hackett" <egroupscdh@...>
> wrote:
> 
> > ... proper fuse settings for a device
> > ... to be shipped as a final product.
> > JTAGEN: Disable to protect the code
> > SPIEN: Disable to protect the code
> 
> Why would you want to disable JTAG and SPI ...

> if you've used the lock bits
> to disable programming and verification?  

By "disable verification", I assume you mean turning off LPM in the
application section in addition to disabling SPM functionality.  I'm
assuming that LPM functionality needs to be left enabled so that the
application code can use flash resident constant data?  Or, does "disabling
LPM" only disable LPM functionality through the On Chip Debug facility and
the application can still access flash data?

> It does no harm, but if a
> device comes back from the field and needs to be rescued, wouldn't you
> want these interfaces active to erase the device and reprogram it?

Hmm, guess you're correct there as long as OCDEN is off. 

... but, then again, if OCDEN is disabled in the field device (as, I assume,
it should be to protect the code).  If I recall correctly, enabling OCDEN
can only be done with a chip-erase which means the code needs to be
re-loaded so one would be debugging the chip and new flash code as opposed
to the code that was in the chip before.

BTW: Still love my Ice-Cube ...
 
Cheers,

Chuck Hackett
"Good judgment comes from experience, experience comes from bad judgment"
7.5" gauge Union Pacific Northern (4-8-4) 844
http://www.whitetrout.net/Chuck