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Technique for Monitoring the State of Inaccessible State Machines

IP.com Disclosure Number: IPCOM000108858D
Original Publication Date: 1992-Jun-01
Included in the Prior Art Database: 2005-Mar-23
Document File: 1 page(s) / 57K

Publishing Venue

IBM

Related People

Cash, RC: AUTHOR [+2]

Abstract

Finite State Machines (FSMs) buried inside ASIC designs are difficult to troubleshoot because their latches are generally not directly observable at module output pins. The device described here takes advantage of unused bus cycles on the ASIC's I/O bus(es) to show the contents of the FSMs in real time.

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Technique for Monitoring the State of Inaccessible State Machines

      Finite State Machines (FSMs) buried inside ASIC designs are
difficult to troubleshoot because their latches are generally not
directly observable at module output pins. The device described here
takes advantage of unused bus cycles on the ASIC's I/O bus(es) to
show the contents of the FSMs in real time.

      Shown in the figure is a block diagram of the general case of
an ASIC employing the FSM monitor technique.  Assume part of the
module's function is to respond to three types of commands:  LOADs,
STOREs and NOOPs.  LOAD commands transfer data from one of the
'internal registers' onto the 'data bus' and STORE commands latch
data from the data bus into one of the internal registers.  A NOOP
command does 'NO OPeration'.  During the NOOP command the data bus is
idle and all devices dotted onto the data bus are assumed to be in
the high impedance mode.

      The figure also shows the blocks necessary to take advantage of
the idle bus cycles that occur during the NOOPs.  When the 'command
decoder' receives a NOOP command it routes one of the banks of FSM
latches through 'MUX 2' out to the data bus.  Input 'FSM bank select'
is used to choose which bank of FSM latches will be routed through
'MUX 1'.  MUX 1 could be eliminated or made wider depending on how
many FSMs are in the module.

      To lower the module's power consumption, during normal
operation the pull-up resistor on '-...