Worked example - design a MOD-6 counter. Step 1: MOD-6 needs 3 flip-flops (2^3 = 8 >= 6) counting 000 to 101. Step 2: detect state 110 (6) with a NAND gate on Qc,Qb (bits: Qc Qb Qa = 1 1 0) and use its output to asynchronously reset all flip-flops. Step 3: sequence: 000->001->010->011->100->101->(110 detected, instant reset)->000. It counts 0-5, six states. Practical note: the reset pulse is a glitch-width spike - fine for LEDs, but for clean synchronous design use a synchronous counter (like 74163) with parallel load instead.