Flip-Flops

A flip-flop is a type of latch that is connected to a clock signal and which executes in time with the clock’s pulse. (Sometimes “latch” and “flip-flop” are used interchangeably but technically a latch is flip-flop without a clock connection.)

JK Flip-Flop

The JK Flip-Flop (the letters are meaningless) is basically an SR latch in functionality. It has a “set” input (J) and a “reset” input (K) and Q and inverted-Q outputs.

Where it differs from the SR is that it the SR will change state just if the voltage is high (this, afterall, is all that a bit is) whereas for the JK to set it must receive a clock pulse and it will only set on the pulse. Hence in addition to J and K inputs it has a CLK input for “clock”.

In addition the JK Flip-Flop has a toggle function. When this is executed, whatever Q currently is will be flipped to its opposite value: \(1 \rightarrow 0\), \(0 \rightarrow 1\). The toggle executes when both J and K are set to high.

The possible state changes for the JK Flip-Flop are detailed below:

A JK Flip-Flop can execute on either the positive or negative pulse. Below are the diagrams for a rising and falling pulse respectively:

T Flip-Flops

Another type of Flip-Flop can be created by connecting the J and K inputs of a JK Flip-Flop to each other. This reduces the possible states to two: toggle current state or maintain current state. Its overall logic is therefore reduced to just two lines of the previous state table: the state that obtains when J and K are \(0 0\) or \(1 1\).

Thus the state table for the T Flip-Flop is: