AVR-Chat

The wiring for setting up the STK500 for parallel mode with a tiny26 can be
found in the help section of Astudio 4.x (not 3.x!) - you will have to dig
around a bit to find it.  It requires a custom 10 conductor cable.

What I do to recover chips that won't ISP program, is to get an SOIC test
clip, bring all wires out to a 20 pin wire-wrap dip and plug that into the
tiny26 socket of the STK500.  Then I can clip on, put the board into
parallel mode and recover the chip.

This isn't guaranteed to work depending upon what is connected to the
various pins of the tiny26.

Cheers!

P.S. I have never had a chip "lock up" in the field, but I have had batches
of chips from the factory with one or more CPUs with the wrong fuse
settings.  Out of four or five hundred CPUs maybe 3 or 4 like that.

What I *have* done, is forget to read/set the fuse settings and start
programming chips (after, say, programming some mega16's) and really messing
up the tiny26.  Once I blew through four or five boards before I figured out
what I was doing wrong :)


-----Original Message-----
From: Ken Holt [mailto:kholt@monitor.net]
Sent: Saturday, November 06, 2004 2:28 PM
To: AVR-Chat@yahoogroups.com
Subject: Re: [AVR-Chat] Fuse gotchas (was Re: STK500 starter kit)



Stefan -
Thanks for your advice - I have assumed that I will be just removing and
replacing the Tiny26, but I was starting to think what other theoretical
possibilities
there were.   For parallel programming, my old STK500 manual doesn't even
mention the Tiny26s, and I'd have to find an adaptor to actually plug it in.
I'm really more concerned about how to keep this lockup from happening
again,
as it seems to have at my client's shop.  I assumed that the SPIEN fuse
had been
disabled by faulty programming, but the spec says that fuse cannot be
changed by
serial mode, nor the RSTDISBL fuse.  My reset pin does still work, since
grounding
it restarts the program.  Also, the internal clock is still selected and
running, so the
device hasn't been accidently set to external clock.
The MOSI and MISO pins are used (during operation) as inputs from a
Cypress USB
chip, and I once thought that maybe those two signals might cause havoc
under the
right circumstance; however SCLK and Reset are both local only to the
ISP header.
I've pulled up MISO and MOSI and connected them only to the ISP header,
with still
no-talkie.

Ken




Stefan Wimmer wrote:

>--- In AVR-Chat@yahoogroups.com, Ken Holt <kholt@m...> wrote:
>
>
>>While skimming and deleting this thread, I have just been
>>
>>
>debugging a
>
>
>>returned
>>board that does seem to have a fuse/lockup problem.  I cannot
>>
>>
>reach the
>
>
>>Tiny26
>>through the ISP (STK500 cable); but the Tiny continues to operate
>>
>>
>it's
>
>
>>pre-downloaded
>>program.  I assume that the serial enable fuse was accidently
>>
>>
>turned off
>
>
>>by someone,
>>and now there is nothing that can be done to load new code.
>>The Tiny is an smt, soldered in place, and even if I could get it
>>
>>
>off
>
>
>>cleanly, I don't
>>think there's any way to place it on the STK500.
>>Should I assume there's no way to move forward?
>>
>>
>
>I had a similar problem lately. What I did was: remove the 'faulty'
>AVR (a Mega8 with accidentially disabled Reset line) using a smd
>repair hot air gun, clean and reflux the board and solder on a new
>one. Not a big story if you have the right tools at hand or know
>someone who has (takes about 2 minutes that way). And not a big loss
>to trash a ~$2 part - what do you pay for a Tiny26 that you are so
>concerned about the thing?
>
>Stefan
>
>
>
>
>
>
>
>
>Yahoo! Groups Links
>
>
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>





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