AVR-Chat

At 07:15 PM 3/29/2005, Graham Davies wrote:


>--- In AVR-Chat@yahoogroups.com, Dave VanHorn <dvanhorn@d...> wrote:
>
> > I haven't looked inside, but my
> > entire use of the Olimex units
> > so far has been at 3V.
>
>My Olimex JTAG ICE used an ATmega16, which is only specified down to
>4.5 volts. Now, in practice it is quite possible that an ATmega16 works
>down to 2.7 volts just as well as an ATmega16L. But, do you want to
>rely on that for a piece of diagnostic equipment that should be beyond
>reproach? Is it good design practice to run an ATmega16 at 3 volts? You
>may have an Olimex JTAG ICE with an ATmega16L or you may be running an
>ATmega16 outside its specified range and not know it.

Well, I guess I'll pop the top and check.
All of these low cost ices are compromise designs, I haven't seen one yet 
that terminates the cable properly like the atmel does.  I also have an 
atmel unit, which I would fall back on if there is any issue.
But, when I ordered these, I had reason to suspect that my jtag had gone to 
pieces, which turned out to be yet another avr studio "vacation day".


>The procedure to load the Atmel software in my Olimex involved taking
>the damned thing apart. This is how I discovered the above. If I hadn't
>noticed the MCU type, I would never have known it was not specified for
>use below 4.5 volts. I do not now trust Olimex as a supplier.

I didn't have to do this. I plugged it in, and it worked.

>While I had the thing in pieces, I inspected the PCB layout. I have
>never seen worse. Ground and power were treated just like any other
>signal and routed all over the place. Again, is this what you want to
>be in the position of trusting while you're debugging sensitive or
>noisy equipment?

Well, I haven't seen the board.  I'm a layout guy myself, and I rarely see 
anything that I like these days.

>I'm not saying you should toss out your Olimex JTAG ICEs. If you're
>happy with them I suppose that's all that counts. I don't know what I
>am saying, really. It just bugs me that a piece of sloppy design like
>this succeeds in the market as well as painstaking and correct design
>because, well, I suppose for the most part it does seem to work.

Well, if there's no operational difference, why would the customer 
differentiate?