Slightly vague question,
but in a nutshell I am wiring up a 595 shift register, and getting really odd results.
I wired it up wire by wire, with power on. I am wondering if perhaps I can mess chips up by connecting wires when they are live. I am powering 8 high output leds which can suck a lot of juice out of the chip, but on the otherhand, I am just connecting arduino outputs that are not THAT powerful...
what's everyone's take? Could I potentially be messing up chips?
thanks,
Lucas
It really depends on the device, and the nature of the mistaken connection.
I had a voltage regulator fail on an Arduino-based system I built - the output voltage was just over 8V when I checked it. (This is pretty horrible treatment of an IC, to go 60% over its rated voltage!) The USB thumb drive and all of the PIC-based pyro sensors died instantly, but the ATmega8, DS1722 and MAX232 seemed unharmed. Since I had spares and did not want the experiment to fail, I replaced the ATmega and MAX232 anyway. I have no doubt that the life of these components was shortened considerably, but they still worked.
Maybe some folks with a deeper understanding of the hardware can offer more info, but in general, the answer is "it depends". 
-j
makes sense.
does stuff usually just fail and stop working or can it begin to act odd? I guess that depends too!
thanks
Both can happen.
I never solder or otherwise work on circuits that are powered. It's very easy to accidentaly short two IC pins when working on a circuit.
When working on a module for my analog synth a couple of years ago i forgot to disconnect power when fixing what i believed was a cold solder joint, during the soldering i shorted two solderpoints on the PCB with the soldering iron and instantly killed two IC's. One of them was discontinued and very hard to come by.
Many IC's will survive this unharmed but some are very sensitive.
MikMo
It doesn't even have to be powered. The ESD from your body can kill them, make them fail early, make them fail with odd symptoms, make the fail early with odd symptoms, etc. Of course wiring stuff up wrong can fry a chip, I've had reasonably good luck with digital chips surviving +5v on any pin but YMMV
I have some 595, if you post your schematic I can breadboard it up and check it. I have perfected my use of the HEF4794B that drives 16 LEDs.
I've abused 595's rather badly.
I actually once had a short in such a way that one output was LOW and it was shorted with a output which was HIGH.
It just got a little hot. Still works fine.
That would probably be the worst thing you can do to it using spec voltages.
All makes sense.
I have some other chips I will be careful with (A SD card writer)
but I have to admit when dealing with the 595 I wasn't all too careful.
Anyhow I restarted from scratch (as far as wiring goes) and got it working.
Only bad thing is I have no idea what was wrong last time.. oh well
thanks guys!