What is Race around Condition?

by Sonali 03/08/2021

Race around condition occurs in JK Flip Flop when both its inputs J=K=1 and also the clock =1 for a long period.

J-K Flip Flop

The truth table is shown below with its circuit diagram.

For J-K flip-flop, if J=K=1, and if clk=1 for a long period of time, then output Q will toggle as long as CLK remains high which makes the output unstable or uncertain.
This is called a race around condition in J-K flip-flop.
We can overcome this problem by making the clock =1 for very less duration.
The circuit used to overcome race around conditions is called the Master Slave JK flip flop.

Here two JK flip flops are connected in series.
The first JK flip flop is called the “master” and the other is a “slave”.
The output from the master is connected to the two inputs of the slave whose output is fed back to inputs of the master.
The circuit also has an inverter other than the two flip flops.
The Clock Pulse and inverter are connected because of which the flip flops get an inverted clock pulse.
In other words, if CP=0 for a master flip-flop, then CP=1 for a slave flip-flop and vice versa.

When the clock pulse goes high, the slave is isolated; J and K inputs can affect the state of the system. The slave flip-flop is isolated when the CP goes low.
When the CP goes back to 0, information is transmitted from the master flip-flop to the slave flip-flop and output is obtained.
As the master flip flop is positive triggered it responds first and the slave later (it is negative edge triggered).
The master goes to the K input of the slave when both inputs J=0 and K=1, and also Q’ = 1. In this case the slave copies the master as the clock forces the slave to reset.
The master goes to the J input of the slave when both J=1 and K=0, Q = 1. The clock is set due to the negative transition of the clock.
There is a state of toggle when both J=1 and K=1. On the negative transition of clock slave toggles and the master toggles on the positive transition of the clock.
Both the flip flops are disabled when both J=0 and K=0 and Q is unchanged.

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