Reducing the Storage Requirements of a Test Sequence by Using One or Two Background Vectors

We describe a storage scheme for functional test sequences where a test sequence
T
is associated with a primary input vector
B
called a background vector.
T
is stored by storing only the differences between its test vectors and
B
. We describe a procedure for computing a background vector
B
for a given test sequence
T
. We also describe a procedure that modifies
T
so as to reduce its storage requirements with respect to
B
. We present experimental results demonstrating that the single background vector
B
, computed based on
T
, allows
T
to be modified such that a vast majority of its entries are equal to the corresponding entries of
B
. Consequently, storage of
T
reduces to storage of a small number of entries. We also extend the discussion to storage of
T
based on two background vectors. A second background vector provides more flexibility in storing
T
as a list of entries where it is different from its background vectors. This contributes to a further reduction in storage requirements for certain circuits.