Page 102 - Understanding Automotive Electronics

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ELECTRONICS FUNDAMENTALS 3

R-S Flip-Flop

An R-S flip-flop circuit A very simple memory circuit can be made by interconnecting two
can be set into either NAND gates, as in Figure 3.9a. A careful study of the circuit reveals that when
state. It will remain S is high (1) and R is low (0), the output Q is set high and remains high
latched in that state until regardless of whether S is high or low at any later time. The high state of S is
it is set to the opposite said to be latched into the state of Q. The only way Q can be unlatched to go
state by the presence of low is to let R go high and S go low. This resets the latch. This type of memory
opposing logic signals on device is called a Reset-Set (R-S) flip-flop and is the basic building block of
its two inputs. sequential logic circuits. The term “flip-flop’’ describes the action of the logic
level changes at Q. Notice from the truth table that R and S must not be 1 at
the same time. Under this condition, the two gates are bucking each other and
the final state of the flip-flop output is uncertain.

Figure 3.9
Flip-Flops

FPO

UNDERSTANDING AUTOMOTIVE ELECTRONICS 89