The protocol chip is responsible for communicating with connected devices, which send the required voltage and current information to the protocol chip. The protocol chip reads the voltage and current information, sends it to the built-in DAC, converts it into an analog signal, sends it to the optocoupler, feeds it back to the device, controls the output of the device, and so on. Protocol chips in many circuits act as bridges to devices, which control whether data can be transmitted between devices or whether one device controls the role of another device.