Killing chips

[mjbcswitzerland]

Hi All

Just wondering whether any one knows whether it is possible to destroy HCS devices by incorrectly deleting Flash?

I have just built a board with the NE64 and I connected it to the debugger. I wanted to download a boot program but wasn't concentrating much - I had seen that the FLASH was not completely blank (I assume it can have a bit of garbage in it when a chip is fresh from the bag). As I said, without thinking I sent a couple of commands to delete the FLASH.
To be exact:
- a write to a FLASH location (any location to prime delete)
- CMD_FLASH_ERASE to FCMD     (prepare erase command)
- CBEIF to FSTAT              (start erase command)

I forgot to set up the Flash clock divide to produce a clock of between 150k and 200k...

Afterwards nothing worked and the board, which was originally consuming a few milli-amperes was taking about 400mA and the NE64 was getting rather hot.

Not concentrating entirely, I don't know exactly whether it all happened when I sent the above command sequence or not but it seems quite likely.

Anyone also managed to produce such destruction? In any case it looks as though I'll have to solder a new one in tomorrow but I don't want to see whether I can repeat what happend.

So any one with similar experience?

Cheers

Mark Butcher
www.mjbc.ch

[eeetee]

hi mark:

the last week i've been writing a lot of "user flash code", anthough i have not actually let the smoke out of a chip by errant clock frequencies, the documentation clearly states that  operating above 200khz will "stress the flash". there is a second criteria that includes the bus clock as well, yielding sort of a convoluted calculation requirement. for some reason, i think that i also read that the internal flash voltage is dependent on the oscillator frequency but i can't find the text right now (could have been an errant firing synapse as well). if that chip is drawing close to a half an amp ... let's have a moment of silence now .. it has passed onto chip heaven.

don't ya hate soldering those qpfs?

regards,

ed

[mjbcswitzerland]

Hi

I soldered in a new device and it works again. I will be more careful in future, including building in a software check before zapping (check that frequency has been programmed correctly).

By the way, soldering in the QFP is not such a big task. Here's how it seems to work best:

1. Place the chip as accurately as possible and solder two corners to fix it
2. Solder all pins making big fat short circuits over every two or three pins, just make sure there's a good contact and lots of solder.
3. Use desoldering braid to suck off as much of the solder as possible (I use SPIRIG 3S-WICK).
4. Check the contacts under a mag. glass to ensure that there are no short circuits under the chip some where (if there are repeat 2..3 for the pins).
After cleaning the flux away, the result looks almost as good as reflow soldering - takes 5 minutes and is surprisingly reliable.

Cheers

Mark Butcher
www.mjbc.ch