Digital Systems: Principles and Design

2

Digital Systems

FIGURE 1.1 (a) A digital circuit consisting of a simple switch. (b) Another digital circuit consisting of a simple switch.

(A) Consider a simple circuit given in Figure 1.1(a). When the switch is pressed, the

voltage at D is +5 V and when released, it is ~0 V. Logic state is true or 1 when the

switch is pressed and false or 0 when released.

(B) Now consider the circuit given in Figure 1.1(b). When the switch is pressed, the

voltage at D¢ is +0 V and when released, it is ~5 V. Logic state is true or 1 when

switch is released and false or 0 when pressed.

1.1.2 Negative Logic

Now let us assume, a logic state 1 represented by a ...