Logic Diagram Of Mod 10 Counter. Nand gate ic 7400 1. So the combinational circuit is designed in such a way that the output y of this circuit becomes 0 to enable the clr reset input of all the flip flops.
The circuit diagram for a mod 12 counter is shown below. To avoid lock out and make sure that at the starting point the counter is in its initial state or it comes to its initial state within few clock cycles external logic circuitry is to be provided and so we design the counter assuming the next state to be the initial state from each unused states. So again 4 flip flops are required.
Circuit excitation table here q 3 q 2 q 1 q 0 are present states of four flip flops and q 3 q 2 q 1 q 0 are next counting state of 4 flip flops.
Decade counters are useful for interfacing to digital displays. It counts from 0 to 9 and again reset to 0. The inputs to the second and third decades come. The state diagram shows that the counter recycles after counting the value 101.