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