Description of Controllers:

These products are designed to help you communicate between different endpoints using different protocols or signaling methods. You'll find devices that connect the I2C bus to a UART, USB to I2C, SPI, Ethernet, or UART, as well as Ethernet MACs and PHYs. Plus, there are devices that help you connect in more than one direction for point-to-point communication interfaces, like USB hub controllers.

What is the difference between a controller and a driver?

A controller is basically a component that connects to the central processing unit (CPU). It manages the flow of data between the CPU and the device it controls, like a printer or disk drive. Controllers usually have a buffer that temporarily stores data from either the CPU or the connected device. On the other hand, a device driver is a software program that tells the controller how to work. Figure 1 shows the difference between a controller and a driver as they're used on a motherboard.