Browse Prior Art Database

Circuit for Detecting Disconnection and Connection of a Pluggable Unite

IP.com Disclosure Number: IPCOM000105134D
Original Publication Date: 1993-Jun-01
Included in the Prior Art Database: 2005-Mar-19
Document File: 2 page(s) / 65K

Publishing Venue

IBM

Related People

Klim, PJ: AUTHOR [+4]

Abstract

Disclosed is a circuit for detecting whenever a pluggable unit, such as the keyboard or mouse, is connected to, or disconnected from, a system unit without turning off electrical power to the system unit. While handling the keyboard, for example, in this way often results in inadver tently switching the scan code output of the keyboard to one which is not supported by the system unit, the output of this detection circuit can be used, for example, to provide signals for resetting the keyboard to provide the proper scan codes after it is plugged in.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Circuit for Detecting Disconnection and Connection of a Pluggable Unite

      Disclosed is a circuit for detecting whenever a pluggable unit,
such as the keyboard or mouse, is connected to, or disconnected from,
a system unit without turning off electrical power to the system
unit.  While handling the keyboard, for example, in this way often
results in inadver tently switching the scan code output of the
keyboard to one which is not supported by the system unit, the output
of this detection circuit can be used, for example, to provide
signals for resetting the keyboard to provide the proper scan codes
after it is plugged in.

       A pluggable unit 10, such as a keyboard or mouse, is connected
to a system unit 12 by a cable 14 having connectors 16 and 18 at its
ends.  Electrical ground within unit 10 is returned to system unit 12
by a ground return line 20 through cable 14, along with contacts in
connectors 16 and 18.  This line 20 is connected to the input of a
buffer 22, along with a voltage VDD through pullup resistor 24.
Buffer 22 is of a type which is used to protect circuits within the
system unit from transients.  The output of buffer 22 is provided as
an input to a latch 26 and to a comparator 28.  The CHANNEL RESET
signal, which occurs during each power-on reset cycle, is provided as
the CLOCK input to latch 26.  The output of latch 26 is provided as
the other input to comparator 28, which  activates a UNIT UNPLUGGED
signal whenever its inputs are unequal.

      During normal operation, with the pluggable unit properly
connected, electrical ground from the unit 10, through line 20, keeps
the input to buffer 22 low, so tha...