Re: What cables can be hot-plugged?

["Michael J. Mahon" <mjmahon@aol.com>]

D Finnigan wrote:
> schmidtd wrote:
>
> > On Oct 9, 3:10�pm, dog_...@macgui.com (D Finnigan) wrote:
> >
> > > schmidtd wrote:
> > >
> > > > On Oct 9, 2:18 pm, dog_...@macgui.com (D Finnigan) wrote:
> > > >
> > > > > Anyone have a list of what cables can be safely hot-plugged?
> > >
> > > > > Specifically, I'm interested in knowing about the: joystick port,
> > > > > serial
> > > > > cable from an SSC, mouse port, and any other similar port.
> > >
> > > > I do Serial and ADB all the time.
> > >
> > > Really? ADB? You must have a lot of guts. I managed to fry the ADB
> > > controller chip on a Mac LC by accidentally hot-plugging it.
> >
> > I have one keyboard with mouse, and a stack of 2 macs and a IIgs; I
> > just yank the plug and move it to the machine I need to use.  I did it
> > a lot while I was working on booting the GS over AppleTalk. :-)
>
>
> Well, look at it from my point of view: I've already fried a Mac! I'm not
> going to risk doing it purposely.

I can certainly understand your reticence.  ;-)

> Anyway, on the IIe, I hot-plugged the joystick and serial cable, (to an
> ImageWriter II) but I turned off the power to plug in the AppleMouse.

In general, if power as well as signals are passed through a connector,
and the connector is not specifically designed to sequence power
properly on hot-plugging, then the connector should neither be plugged
nor unplugged with power on.

There is ample testimony here to the fact that you can get away with
it with some connectors all of the time, and all connectors some of
the time, but you can't get away with it with all connectors all of
the time!

There is a specific problem related to hot-plugging (not unplugging)
that should be mentioned:  electrostatic discharge.

If you have just walked across a room or slid in your chair with a
keyboard connector to plug it into a system, your body capacitance
may be charged to several thousand volts relative to ground.  If the
first low-impedance contact you make with the system is the connector,
then your capacitance will discharge through the closest pin, possibly
damaging any IC connected to it.

If you must hot-plug, touch something connected to the system ground
with one hand before actually approaching the connector--it can save
you a lot a trouble.

-michael

NadaNet and AppleCrate II: parallel computing for Apple II computers!
Home page: http://home.comcast.net/~mjmahon

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