State Diagram of Decade Counter

we observe the decade counter circuit diagram, there are four stages in it, in which each stage has single flip flop in it. So it is capable of counting 16 bits or 16 potential states, in which only 10 are used. The count starts from 0000 (zero) to 1001 (9) and then the NAND gate will reset the circuit.

Multiple counters are connected in series, to count up to any desired number. The number that a counter circuit can count is called "Mod” or "Modulus”. If a counter resets itself after counting n bits is called "Mod- n counter” "Modulo- n counter”, where n is an integer.

The Mod n counter can calculate from 0 to 2n-1. There are several types of counters available, like Mod 4 counter, Mod 8 counter, Mod 16 counter and Mod 5 counters etc