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Digital Circuits and Logic Design
Notes and F′ = A′B + A′C + AB′C′
2
The minimum number of product terms is (4) and is obtained if we implement F1 in complement
form and F2 in true form.
The following PLA programming table is used.
Table 8.1: PLA Programming Table
Inputs Outputs
Product terms A B C F F
1 2
1 B′C′ – 0 0 1 –
2 AB 1 1 – – 1
3 A′BC′ 0 1 0 1 1
4 AC 1 – 1 1 –
True/Complement → T C
8.8.2 Programmable Array Logic (PAL)
PAL has a fixed array of OR gates and programmable array of AND gates. It is easier to program
than the PLA but is less flexible. It is suitable to implement a number of Boolean functions which
have no or a few overlapping product terms.
The logic diagram of a typical PAL is shown in the following Figure 8.13.
Figure 8.13: PAL Logic Circuit
When we implement Boolean functions with PAL, we must simplify the functions to fit the sections
of the PAL. A product term cannot be shared among two or more OR gates. If the function cannot
fit in one section, then we may use two sections to implement the function.
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