This next section will discuss how the detection of an object on the pad, and the communication from the object back to the pad works. First, the TX controller has to detect the presence of an object placed on the pad. This is done using an “analog ping” in which a short pulse is generated from the TX pad. If there is no object on the pad, the primary coil voltage will be high since it is unloaded. However, if any electrical load is detected, the primary coil voltage will be lower, which allows detection of an object. If the analog ping indicates that a device is sitting on the pad, a longer pulse, or “digital ping” is generated by the TX pad – this generates enough energy to power up the RX side circuits, which will then send a communication packet back to the TX processor to identify itself. Only when the proper communication is established, the TX processor will begin to generate power out on the primary coil. Since all Qi compliant devices use the same protocol, interoperability is assured. The RX side sends “control error packet” messages back to the TX side – this tells the TX how much power to put out, and only as much power as required will be sent.