disconnecting keyboard: big trouble !?!

[Chris Pressey]

On Tue, 23 Mar 2004 10:44:11 -0600
Nathan Kinkade <nkinkade at ub.edu.bz> wrote:

> Can anyone on the list point me to a manufacturers site or
> documentation that unequivocally states in clear terms the real
> dangers of hotplugging a PS/2 device?

How about http://www.heurtley.com/richard/maintenance.html ?

It's basic electronics - plugging or unplugging anything from a powered
device has a greater-than-zero chance of frying it.  The difference
between "hot-pluggable" USB and "risky" PS/2 can be summed up like so:

re USB: "A USB transceiver is required to withstand a continuous short
circuit of D+ and/or D- to VBUS, GND, other data line, or the cable
shield at the connector, for a minimum of 24 hours without degradation.
It is recommended that transceivers be designed so as to withstand such
short circuits indefinitely. The device must not be damaged under this
short circuit condition when transmitting 50% of the time and receiving
50% of the time (in all supported speeds)."
  -- http://www.usb.org/developers/docs/usb_20.zip
     (a standards document - note "required" and "must not be damaged")

re PS/2: "Vcc/Ground provide power to the keyboard/mouse.  The keyboard
or mouse should not draw more than 100 mA from the host and care must be
taken to avoid transient surges.  Such surges can be caused by
"hot-plugging" a keyboard/mouse (ie, connect/disconnect the device while
the computer's power is on.)  Older motherboards had a surface-mounted
fuse protecting the keyboard and mouse ports.  When this fuse blew, the
motherboard was useless to the consumer, and non-fixable to the average
technician.  Most newer motherboards use auto-reset "Poly" fuses that go
a long way to remedy this problem.  However, this is not a standard and
there's still plenty of older motherboards in use.  Therefore, I
recommend against hot-plugging a PS/2 mouse or keyboard."
  -- http://panda.cs.ndsu.nodak.edu/~achapwes/PICmicro/PS2/ps2.htm
     (note "not a standard")

-Chris