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Browse Prior Art Database

Driver Enable Control

IP.com Disclosure Number: IPCOM000103046D
Original Publication Date: 1990-May-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 1 page(s) / 41K

Publishing Venue

IBM

Related People

Fuhs, RE: AUTHOR [+4]

Abstract

Described is a method which allows transferring of address and data using an architecturally constrained instruction.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 100% of the total text.

Driver Enable Control

      Described is a method which allows transferring of address and
data using an architecturally constrained instruction.

      Turning off system clocks of a chip results in a latch being
set to prevent undesirable results when the clocks are restarted if
the chip is in a dangerous state.  The chip effectively knows when
its clocks have just been started and determines that its logic is in
a safe state before allowing its logic to control its outputs.

      An override latch was implemented on a VLSI chip which
prevented it from driving shared control lines regardless of the
state the chip logic is scanned to.  This latch is configured such
that it is not a scannable by a service processor.  Therefore, it can
never be altered through scanning.  It is set active whenever the
service processor stops the clocks on the chip.  (The clocks are
always stopped before a scan operation is performed on a chip.) The
override latch is reset when the service processor restarts the
clocks on the chip and the chip's logic that normally controls the
shared lines is in the proper disabled state. (See Fig. 1.)  If the
chip logic is not in the proper state to keep the shared lines
disabled, then the override latch will not be reset and will prevent
the chip from driving these lines. (See Fig. 2.)

      Disclosed anonymously.