Ripple Counter - Circuit Diagram, Timing Diagram, and Applications
Synchronous counter
How to design a synchronous counter 4 bit using JK flip flop that can count up even numbers from 0 to 14, and count down odd numbers from 15 to 0 in 1 system - Quora
Synchronous counter
Synchronous 4-Bit counter circuit using JK-flip-flops | TikZ example
Synchronous Counter and the 4-bit Synchronous Counter