In Logism, I have a logic circuit for a 74157 IC with Inputs (A1, A2, A3, A4 & B1, B2, B3, B4) and the outputs (Y1, Y2, Y3, Y4) are attached to two 7 Segment Displays and I need to implement a clock and observe what happens when the tick time is varied. Where do I implement the clock? I also have Select & Strobe connected to the circuit.