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# Saving of the Error State During Control Failures

IP.com Disclosure Number: IPCOM000111611D
Original Publication Date: 1994-Mar-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 2 page(s) / 55K

IBM

## Related People

Haess, J: AUTHOR [+4]

## Abstract

One problem with logic circuits which have a control function is that after certain unforeseen circumstances, the state of the circuit may be changed. In such cases it is often not possible to determine the reason for the change in the circuit state even if one stops the system clock. To allow a better understanding of the causes of the errors, the logic of the circuit may be extended by a function which continually records the state of the circuit and, in the event of an unallowed change of the circuit's state, maintains a record of the previous state of the circuit. This allows a better analysis of the reasons for the malfunctioning of the circuit since all the information is provided to determine how and at what point the error occurred.

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Saving of the Error State During Control Failures

One problem with logic circuits which have a control function
is that after certain unforeseen circumstances, the state of the
circuit may be changed.  In such cases it is often not possible to
determine the reason for the change in the circuit state even if one
stops the system clock.  To allow a better understanding of the
causes of the errors, the logic of the circuit may be extended by a
function which continually records the state of the circuit and, in
the event of an unallowed change of the circuit's state, maintains a
record of the previous state of the circuit.  This allows a better
analysis of the reasons for the malfunctioning of the circuit since
all the information is provided to determine how and at what point
the error occurred.

The implementation of the extra logic function is shown in the
Figure and consists of three elements:

o   A control element 3 which can be described in terms of a finite
state machine.  The control element 3 comprises a state register

4 and logic to produce the output signal and logic to determine
the following state of the circuit.

o   A back-up register 9 which records the state of the circuit prior
to the error occurring.

o   An error detecting circuit 5 to detect errors in the control
element 3 and to freeze the state recorded in the back-up
register 9.

The control element 3 controls the logical fun...