146_pdfsam_VLSI TEST PRINCIPLES &amp; ARCHITECTURES

# 146_pdfsam_VLSI TEST PRINCIPLES &amp; ARCHITECTURES -...

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Logic and Fault Simulation 115 3.2.3.1 Truth Tables Using the truth table is the most straightforward way to evaluate logic elements. Assuming only binary values, an n -input combinational logic element requires a 2 n -entry truth table to store the output value with respect to all possible input combinations. (For a sequential element, n corresponds to the number of its input and state variables.) In practice, the truth table is stored in an array of size 2 n .To access the array, the values of the n input variables are packed in a word that serves as the index to access the array. For example, consider the array T NAND3 to store the truth table of a three-input NAND gate. Then, the output value with respect to input pattern 010 is obtained by: T NAND3 ± 010 2 ² = T NAND3 ± 2 ² where the subscript 2 indicates the binary number system. For a multivalued logic system with k symbols, the required array size for an n -input element is calculated as follows. Let m be the number of bits needed to code the k
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