Serial resistors in matrix keypads are used to reduce the number of connections required between the keypad and the logic circuit. In a standard matrix keypad, each row and column is wired separately to the logic circuit. This means that there are as many wires going into the keypad as there are columns and rows. With serial resistors, only one wire is needed for each column and row. This reduces the number of wires by a factor of N (where N is the number of columns or rows in the keypad). It also makes wiring the keypad easier, since there are fewer...