The principle of a basic I/O port expander is that it provides additional I/Os
that can be used by the host processor to implement additional features such as increased number of inputs/outputs, expanding the number of control signals
and mixed signal lines
controlling a greater number of peripherals without resorting to an
additional Complex Programmable Logic Device (CPLD) or upgrading the
central processing unit (CPU).
Xpander logic include an advanced matrix keypad
supporting up to 96 keys and an advanced PWM controller
providing complex brightness pattern control.
The Xpander home page is here