Browse Prior Art Database

Automatic Trace Multiplexer Control

IP.com Disclosure Number: IPCOM000111642D
Original Publication Date: 1994-Mar-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 2 page(s) / 73K

Publishing Venue

IBM

Related People

Haess, J: AUTHOR [+2]

Abstract

For complex logic chips, it is very difficult to determine from the outside what is happening within the chip. One must therefore use some of the very few chip Input/Output (I/O) pads which are not required functionally to obtain information about the internal state of the chip. This article describes a method which allows the particularly effective use of these chip I/O pads as trace outputs. The method involves adding an output multiplexer between the outputs of the logic blocks in the chip and the trace outputs. The multiplexer is controlled by an internal mechanism which automatically selects the active outputs of the logic blocks and switches this output to the trace outputs.

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Automatic Trace Multiplexer Control

      For complex logic chips, it is very difficult to determine from
the outside what is happening within the chip.  One must therefore
use some of the very few chip Input/Output (I/O) pads which are not
required functionally to obtain information about the internal state
of the chip.  This article describes a method which allows the
particularly effective use of these chip I/O pads as trace outputs.
The method involves adding an output multiplexer between the outputs
of the logic blocks in the chip and the trace outputs.  The
multiplexer is controlled by an internal mechanism which
automatically selects the active outputs of the logic blocks and
switches this output to the trace outputs.

The implementation of the idea requires four elements:

o   a controllable output multiplexer,

o   a programmable control register,

o   an observable chip controller, and

o   control logic for the above elements.

      The output multiplexer is able to pass several output signals
simultaneously in different combinations to the periphery of the chip
and thus make the signals observable to the outside world.  The
selection of which output signals are passed is made by selection
signals from the control logic.  The programmable control register is
designed to allow the tester of the chip to choose which selection
signals are issued from the control logic.  The chip controller
controls the logic function of the chip.  The operations of the logic
blocks of the chip are described in terms of finite state machines.
The control logic controls the output multiplexer and is dependent on
several conditions.  These conditions may be programmed into the
control register.

      The essential novel featur...