Partially complete Function
Duration: 3 min
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The video lecture focuses on the digital logic concept of 'Partially Functionally Complete' functions. The instructor defines this property as the ability to implement any digital circuit using a specific function, with the constraint that logic 0 or 1 can be used as input lines, but complemented forms of inputs are not allowed. He uses the function f(a,b) = a' . b as a case study to demonstrate how to verify this property through algebraic manipulation.
Chapters
0:00 – 2:00 00:00-02:00
The instructor begins by writing the formal definition on the whiteboard: 'A function is said to be partially functionally complete, if it can be implement any digital circuit with support of logic 0 or 1 as a input line (can't use complemented form).' He introduces the specific function f(a,b) = a' . b and systematically evaluates it under different input conditions. He first checks f(a,a), which results in a' . a = 0. Next, he evaluates f(a,0), yielding a' . 0 = 0. Finally, he calculates f(a,1) = a' . 1 = a'. This last step is critical as it proves the function can generate a NOT gate (inverter) by simply tying one input to logic 1.
2:00 – 3:16 02:00-03:16
Moving to the right side of the board, the instructor analyzes the nested expression f(f(a,1), b). He substitutes the previously derived result, replacing the inner f(a,1) with a'. This simplifies the expression to f(a', b). By applying the original definition f(x,y) = x' . y, he substitutes a' for the first variable, resulting in (a')' . b. The double negation cancels out, leaving a . b. This derivation proves that the function can implement an AND gate. Since the function can generate both NOT and AND operations, it satisfies the criteria for being partially functionally complete.
The lecture effectively bridges the gap between abstract definitions and practical circuit implementation. By breaking down the function f(a,b) = a' . b, the instructor demonstrates that partial functional completeness relies on the availability of constant inputs to generate fundamental logic gates like NOT and AND. This capability allows the construction of any complex digital circuit, provided the specific constraints regarding complemented inputs are respected. The step-by-step algebraic proof serves as a template for analyzing other functions for this property.