Page 109 - Handout Digital Electronics

The JK Master-Slave flip flop operates as follows:

On a 1 to 0 clock transition, the master flip flop is connected to the JK input lines, and the slave is
inhibited from operating because of the NOT gate that complements the clock signal to the slave flip
flop. On a 0 to 1 clock transition, the master is isolated from the input lines, and the slave is activated,
and the contents of the master are transferred to the slave flip flop. The purpose of the slave is to hold
the output of the master whilst it is being set for the next input as determined by the J and K inputs.

JK Master-Slave flip flop Truth Table

C J K Q* Q * Q Q Meaning

1 0 0 0 1 0 1 No change
1 0 1 0 1 0 1 Clear to zero
1 1 0 1 0 1 0 Set to one (store)
1 1 1 0 1 0 1 Toggle

The JK master-slave eliminates the problem of toggling more than one, but it is expensive. The edge
triggered flip flops have been developed to replace them in some instances, especially the edge triggered
JK flip flop which has become universal and most widely used flip flop. The JK flip flop, because of
its
Toggling nature is used to implement binary counters. The Q* and Q * are the outputs of the master JK.
From the truth table the master JK operates in the same way as the conventional JK flip flop. The
Feedback is only used in the input combination C = J = K =1.

Figure 45: JK master-slave with simulated signals where the previous state was Q = 1, and not Q ( Q ) =
0.

13.3 The T (Toggle) Flip Flop
The T (toggle) flip flop changes its output on each clock edge, giving an output which is half frequency
of the signal to the T input. For example:

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