3 USB Type-C DRP

In USB Type-C, the role of a port is determined by the state of the CC1 and CC2 pins. A peripheral port has pulldown resistors Rd from CC1 and CC2 to ground. A host port has pullup resistors Rp to VCC. This is shown in Figure 3-1. The values of Rd and Rp are governed by the USB Type-C standard. The host can use the value of Rp to advertise current available on the VBUS pin: 0.5 A, 1.5 A or 3 A.

A DRP periodically toggles CC1 and CC2 between Rp pullup to VCC and Rd pulldown to ground over a period of 50 ms to 100 ms, as defined in the USB Type-C standard. When connecting an external host to a DRP, the connection is detected during the interval of Rd pulldown and the DRP assumes a peripheral role (upstream-facing port). When connecting an external peripheral to a DRP, the connection is detected during the interval of Rp pullup, and the DRP assumes a host role (downstream-facing port).