What Is an IO Expander?
An IO expander is a semiconductor device that functions as a peripheral integrated circuit (IC) for a microcontroller. It is used to increase the number of IO ports available to a microcontroller, which often has a limited number of pin terminals.
This approach allows for cost-effective microcontroller usage in basic products by minimizing pin numbers, while also enabling the same microcontroller to support high-end products through IO expansion. The IO expander thus plays a crucial role in enhancing the system’s overall expandability and versatility.
Uses of IO Expanders
IO expanders are particularly valuable when the built-in IO ports of a microcontroller are insufficient for an upgraded or expanded system functionality. They are used to augment the available IO ports without needing to redesign the entire system. Common applications include controlling a 7-segment LED, which requires numerous control pins, and serving as versatile input/output ports. However, they are generally unsuitable for high-speed IO port switching or data reading due to their typical use of serial buses like the I2C bus.
Principles of IO Expanders
Controlled via a serial bus such as the I2C bus, IO expanders usually come with 8-bit or 16-bit IO ports. A microcontroller configures these ports as input or output by setting the direction register in the IO expander. Data is then written to or read from the port input/output register. When configured as an output port, the IO expander outputs data from each port; when set as an input port, it can read data from the specified input port.
Additionally, some IO expanders feature an interrupt input terminal. When a pre-set condition is met, an interrupt output is activated, which can be connected to the microcontroller’s interrupt input. This feature enables the microcontroller to respond instantly to external events, enhancing system control and responsiveness.