• Passive NPSF (PNPSF)

PNPSF implies that a certain neighborhood pattern prevents the cell under test from changing its value. An PNPSF is represented as

, where is the value in the cell under test, represent the values in the neighboring cells and represents fault effect in the cell under test. There can be three types of PNPSF:

•  : cell under test cannot be changed from 0 to 1 (initial value of cell under test is 0)
• : cell under test cannot be changed from 1 to 0 (initial value of cell under test is 1)
• : cell under test cannot be changed regardless of content.

In the above discussion of NPSFs we have taken only type-1 neighborhood, however, these models can be easily extended to type-2 neighborhood by increasing the number of cells in the NPSF representation accordingly.

2.6  Address decoder faults

Row and column decoder blocks of Figure 1 comprise the address decoder. As discussed before these blocks are composed of logic gates. However, their testing and fault models are different from that used to test circuits made of logic gates. From the context of memory testing four types of faults are considered in address decoder (for both reading and writing) [1]

•  No cell is accessed for a certain address

•  No address can access a certain cell

•  With a particular address, multiple cells are simultaneously accessed

•  A particular cell can be accessed with multiple addresses.

In the next section we will discuss test techniques for the fault models discussed.