With four T flip-flops in a chain you build a 4-bit counter. The inverted output of a T flip-flop is connected to the input of the next T-flip-flops...

Each time you press the pushbutton switch **S1**,
the 4-bit counter counts from **0** to **15**,
before it falls back to **0**.
Therefore it is referred to as a **modulo-16**
or **mod-16 counter**.

The result is displayed as a **binary number**
by **Q0**
to **Q3**.

In the next experiment,
you get to know more **modulo-x counters**...