3.2.1

Shift Register It passes digit to higher digit every time when the clock strikes from 0 to 1. When the "Set_to_15" button is strikes from 0 to 1, it sets all four digits to 1, so the output number is 15 or "F" on the hex display. When the clear button is stroked from 0 to 1, it sets all four digits to 0, so the output number on the hex display is 0.