1.1. GPIO Pin Expansion and I2C
In some cases, it may be required to have access to the GPIO pins from a relatively long PCB trace path within the system (such as in the two different parts of a clamshell cell phone). Because the I2C interface is a two-wire system, the design provides multiple input and output pins at the remote end with just a common two-wire trace. This provides increased design flexibility and also adds to the physical compactness of the entire system. It also enables smaller packaging and a reduced pin count. Devices such as fan controllers, LED status displays, and status indicators can be easily connected and controlled via the general purpose output pins. Similarly, devices such as reset pins and push button switches can be easily coupled to the general purpose inputs provided on the device to serve various applications.
Figure 1. GPIO Pin Expansion via an I2C Bus