The keypad rows are scanned one by one, and their state is stored into a local 16-bit register. Each bit in the register corresponds to one key on the keypad.
The output of the 16-bit register is then converted to the 7-segment display with some simple combinatorial logic.
There are no debouncing, latching or some other advanced features.
Connect a keypad (take a look at the pinout table below), reset the hardware, and start pressing the keypad keys. The corresponding numbers, and characters, should be shown on the 7-segment display.
Keypad matrix 4x4. For example:
