T flip flop

This type of flip-flop is a simplified version of the JK flip-flop. It is not usually found as an IC chip by itself, but is used in many kinds of circuits, especially counter and dividers. Its only function is that it toggles itself with every clock pulse (on either the leading edge, on the trailing edge) it can be constructed from the RS flip-flop as shown in Figure 2.10 (a).

Figure 2.10: The T flip flop

This flip flop is normally set, or ``loaded'' with the preset and clear inputs. It can be used to obtain an output pulse train with a frequency of half that of the clock pulse train, as seen from the timing diagram, Figure 2.10 (b). In this example, the T flip flop is triggered on the falling edge of the clock pulse.

Several T flip-flops are often connected together in a simple IC to form a ``divide by N'' counter, where N is usually 5, 10, 12 or a power of 2.

source : http://web.cs.mun.ca/~paul/cs3724/material/web/notes/node15.html