When this circuit is built I should be able to inject the XTAL pin on my Atmeg8 with the output of this circuit which will then allow me to reset the fuse bytes. Am i correct so far?
Greetings konguk,
Yes! and Yes!
I’d make three suggestions: Firstly, the unused gates should
be tied-off (to prevent them from oscillating or latching up
in a way that may damage the IC).
Secondly, with five unused inverter gates for free (in the
single package) you can use one as a buffer for the output
signal.
Also, add a supply by-pass capacitor to pins 14 and 7, as
close as practical to pin 7. Any small value ceramic (10 to
100nF) will work. Most of us have candidates in the "junk
pile" or salvage from almost any junk computer boards
on hand.
Unused gate problems can be fixed as follows:
(1) Connect pin 11 to pin 12 and take the signal output
from pin 10.
(2) Connect pin 1 to 14 (+5V), connect pins 2 and 3, and
connect pins 4 and 5 and finally, pins 6 and 9. This step ties
off the four unused gated from possible oscillation.
inventore123:
To rescue the failed chips you only need a breadboard and a 2…8MHz crystal or better still an oscillator as described from bigglez. Connect the programmer, a power supply and restore the fuses to the default value that can be found in the datasheet.
konguk et al.,
FWIW, I “locked up” an AVR chip this week. Pilot error…
Had to put the dead AVR back in the STK500 board and
lash in the STK500 on board oscillator and use parallel
Spotted it just after I posted that last message! Hopefully my components will arrive today so i can build the circuit and, fingers crossed, reset the fuse bytes on my Atmega!
Right after a bit of a break im back and trying to build the circuit from start again using breadboard. Im going to post some parts of it up to ensure im doing things right as im going along.
Can someone please check and see if this layout matches my shcematic?
Thought i’d ressurect this thread as it’s related! Didn’t end up getting anywhere with the boards, also failed miserably at reseting the fuse bytes.
I’m now about ready to try again but wanted to be a bit more prepared so am looking at buying a programmer that is capable of resetting the fuse bytes and rescuing a load of atmega8 chips, also want the ability to program different atmels in the future.
Would i be able to reset fuse bytes with this programmer and is it a good deal?
I am also looking to get my hands on a basic oscilloscope as it’s looking like an essential bit of kit! I don’t know too much about my requirements but thought something like http://cgi.ebay.co.uk/OSCILLOSCOPE_W0QQ … dZViewItem might be suitiable?
Hope someone can steer me in the right direction, thanks…
konguk:
I was looking at an STK500 which looks good for the price, found this one… Would i be able to reset fuse bytes with this programmer and is it a good deal?
The STK500 is fantastic! I started learning about the AVR
uC on one years ago, and use it to this day for programming
the odd chip or testing out a simple hardware prototype.
I don’t have the add-on cards (yet) as I only use the DIP
packaged AVRs with it. I can’t vouch for the price in the UK.
You will need a PC (to run AVR Studio software) with a
serial com port.
konguk:
I am also looking to get my hands on a basic oscilloscope as it’s looking like an essential bit of kit! I don’t know too much about my requirements but thought something like …might be suitiable?
I'm a big fan of Leader analogue scopes (I have an LBO518,
see PIX earlier in the thread). The one on eBay is a lesser
model but certainly a good starter 'scope. Good luck bidding!
Right, finally recieved my Atmel STK500 programmer, took a while to arrive but it was a bargain price at 50GBP
Managed to rescue my chips after I spent ages battling with the user manual!
I have set the fuses correctly now and managed to flash the Atmega8 with the firmware, after reading it back it looks the same but the end of the HEX file has lots of extra FFFFFFF’s! Is this just empty space on the Atmega?
Although my Atmega8 is now correctly flashed and has the correct fuse bytes, the circuit still doesnt work
I have attatched a schematic (Which is correct) and my breadboard (Where the problem lies) and was wondering if anyone would be so kind as to give it a once over and see if I have made any obvious mistakes?
konguk:
I have set the fuses correctly now and managed to flash the Atmega8 with the firmware, after reading it back it looks the same but the end of the HEX file has lots of extra FFFFFFF’s! Is this just empty space on the Atmega?
Yes.
konguk:
I have attatched a schematic (Which is correct) and my breadboard (Where the problem lies) and was wondering if anyone would be so kind as to give it a once over and see if I have made any obvious mistakes?
(1) Move the 1K5 resistor from ground to the +5V rail
(2) The uC Reset (pin 1) should be tied to 5V (10K resistor)
(3) Add a decoupling cap across the Vcc and Gnd rails
(4) All resistors appear to 22k (or, is this just a graphics error?)
(5) Check that top and bottom rails on the protoboard are linked
