Page 114 - Handout Digital Electronics

LECTURE 14 EDGE TRIGGERED FLIP FLOPS
14.1 Positive edge transition and negative edge transition

The edge triggered flip flops were developed to eliminate the JK flip flop problem of toggling more than
once. The JK master-slave flip flop eliminates this problem, but it is expensive. The edge triggered flip
flops operate either on the rising edge of a clock pulse (positive edge transition) or on the falling edge of
a clock pulse (negative edge transition). For example:

Figure 48: Positive edge transition

When the positive edge transition threshold is reached, the inputs are locked out, and the flip flop
becomes irresponsive to any further inputs and will only accept inputs on the next positive edge
transition.

Positive edge triggered flip flop symbol

In some cases, the not Q ( Q ) output will not be shown; this is because data or information is collected
at the Q output of flip flops. But it does not mean that it is important. In counters, it is used for down
counting where the clock is connected to it to complement the original clock signal. Positive edge
transition is also known as a trailing edge of the clock pulse or the rising edge of the clock pulse
transition or 0 to 1 transition.

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