A flip-flop or latch is a circuit that has two stable states and can be used to store state information.

If the T input is high, the T flip-flop changes state ("toggles") whenever the clock input is strobed. If the T input is low, the flip-flop holds the previous value.

T flip-flop operation
Characteristic table Excitation table
T Q Qnext Comment Q Qnext T Comment
0 0 0 hold state (no clk) 0 0 0 No change
0 1 1 hold state (no clk) 1 1 0 No change
1 0 1 toggle 0 1 1 Complement
1 1 0 toggle 1 0 1 Complement

Truth Table

When T is held high, the toggle flip-flop divides the clock frequency by two; that is, if clock frequency is 4 MHz, the output frequency obtained from the flip-flop will be 2 MHz. This "divide by" feature has application in various types of digital counters. A T flip-flop can also be built using a JK flip-flop (J & K pins are connected together and act as T) or a D flip-flop (T input XOR Qprevious drives the D input).

Symbol