Re: What cables can be hot-plugged?

[Michael Black <et472@ncf.ca>]

On Sat, 9 Oct 2010, 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.
There's two issues here.  Whether the plugging in while alive will damage
the hardware, and then whether the device will be recognized if it's not 
in place when the computer is turned on.

The Apple II is pretty "dumb" so probably there isn't much that needs to 
be in place only on power up.  On the other hand, that dumbness means
it isn't likely to notice when something new is plugged in, so there may 
not be the needed initialization.

Devices that need power from the computer are likely the things to be most 
damaged.  You can't count on things connecting in the proper sequence; if 
something gets signal before it receives needed power, it is possible to 
damage the input.  I seem to recall that the USB connector has the power
and ground pins longer than the data pins, which helps to ensure that the 
external device has power before any signal gets to it.

Note that MIDI connectors are likewise "safe" because they get no DC 
connection to the device it is plugged into, there's an optocoupler 
invovled to transfer the signal.

A serial connector should be perfectly safe, I've never worried.  A 
relative few signals, and generally sturdy interface to connect to and 
from between RS232 and TTL.

As I write this, I realize I might be hesitant about parallel ports (and 
probably most likely printers), but I suspect that's more because there 
are a lot more signals than on a serial port, which then just increases 
any chance that something might get damaged.

Joysticks, they are just resistors and switches, they aren't going to harm 
anything.  Note that the default state is having nothing connected, which 
means the joystick controllers work fine with nothing connected.

I'd worry about initialization with a mouse, would it recognize that a 
mouse is now plugged in?  But then without knowing what's involved in the 
interface, I guess I'm assuming a more complicated interface than the 
Apple II is likely to have.

I never had much ADB so I wouldn't have plugged things in and out.  But 
then, with only one mouse and keyboard when I ran an Mac, not only did I 
have no reason to consider unplugging them while the computer was on, I 
might worry especially of doing damage.  When spares aren't around or 
cheap, one does think twice.

I wouldn't plug a board in while power was on.  It doesn't matter that 
some people have done it, I sure wouldn't.  On the other hand, I seem to 
recall instances of plugging something in somewhere and then noticing that
the power was still on, but that sure wasn't deliberate.

   Michael