Direct Implementation

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Direct Implementation

Consider the function

$\begin{displaymath}f(A,B,C) = \sum m(2,3,6,7) \end{displaymath}$

expressed in canonical SOP form. Then assuming all variables and their complements are available we can implement this function with the AND-OR circuit of Figure 24.

**Figure 24:** AND/OR implementation.
$\begin{figure} \begin{center} \epsfig{file=images/diglogimg14.eps}\end{center}\end{figure}$

This implemntation is not minimal in general (i.e. can realize f with fewer gates).

This representation is direct and is useful when implementing with programmable logic devices (PLD). To illustrate, consider functions f=f(A,B) of two variables (n=2, 2ⁿ=4). A PLD schematic is shown in Figure 25.

**Figure 25:** PLD implementation.
$\begin{figure} \begin{center} \epsfig{file=images/diglogimg15.eps}\end{center}\end{figure}$

This PLD can program any given function f(A,B) by breaking appropriate links.

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