In the keypad HDL encoder, NANDing of the columns is used to activate the freeze bit.

In HDL when a circuit is simulated on a computer, the designer must create all the different scenarios that will be experienced by the actual circuit and must also know the proper response to those inputs.

In the keypad HDL encoder, the freeze bit detects when a key is released.

In the keypad HDL encoder, after releasing a key the ring counter resumes its counting sequence.

In the digital clock project, when it is 11:59:59, AND gate 1 detects that the tens of hours is 1 and the edge trigger clock moves the display to 12:00:00.