4x4 matrix keypad useful for making various password based applications, Motor controlling applications, similar to phone keypad.
A 4x4 matrix keypad requiring eight Input/Output ports for interfacing issued as an example. Rows are connected to Peripheral Input/Output (PIO) pins configured as output. Columns are connected to PIO pins configured as input with interrupts. In this configuration, four pull-up resistors must be added in order to apply a high level on the corresponding input pins