Models in Memory Testing - Models in Hardware Testing - page 164

FP D < SOS = FB > (6.1)

The SOS represents the sensitizing operation sequence and includes the initial data
C stored in a set of memory cells involved in the target fault, followed by an op-
tional sequence of memory operations to be performed in order to sensitize the fault
(Eq. 6.2 ) . The cells initialized and accessed during the SOS are denoted as f-cells.

SOS D .C; op 1 op 2 ::: op m /; with m 0 (6.2)

where:
C D s f cell 1 s f cell 2 :::s f cell k . s f cell i 2 f 0; 1; g denotes the content of
the f-cell with address f - cell i ,and' ' denotes a don't care condition in which
the initial value of the cell is not relevant;
op i 2f r Œd ; w i d g . w i d ,whered 2f 0; 1 g , represents a write operation of the value
d on the cell with address i while r Œd represents a read operation of the content
of the cell with address i . If the optional value d is specified, it is interpreted
as the expected value returned by the read operation and the operation itself is
denoted as a read and verify operation.
The sequence of memory operations can be omitted when the faulty behavior is
sensitized just by the f-cells being in a certain condition (e.g., State Coupling fault
( Dekker et al. 1990 ) ).
Examples of SOSs are:
SOS D 0 i : It corresponds to an FB sensitized by the state of the f-cell with
address i equal to 0.
SOS D ; w i 1 : It corresponds to an FB sensitized by writing 1 into the f-cell with
address i , regardless the current state of the cell.
SOS D 1 i ; w i 1 r i : It corresponds to an FB sensitized by a write operation of the
value 1 on the faulty cell with address i immediately followed by a read operation
of the content of the same cell. In this case the FB is sensitized only if the two
operations are applied when the cell i initially contains the value 1.

FB (Eq. 6.1 ) identifies the behavior of the faulty memory with respect to the fault
free one. In the early 1980s, and during the first part of the 1990s, the only element
considered relevant for the definition of a faulty behavior was the logic state stored in
the memory cells ( Van de Goor 1991 ). Starting from the end of the 1990s, due to the
increased memory complexity the output value of a read operation started to be rel-
evant to correctly describe realistic and observed fault models ( Van de Goor 1999 ) .
An FB can be expressed using the notation of Eq. 6.3 .

F=R (6.3)

where

f f cell 1 f f cell 2 :::f f cell k ; with f

F D 2f 0; 1 g (6.4)