Ruigu Electronic

OTG has been renamed to Dual-Role Port, with a new method for role determination.

2025-11-19

Within the Type-C ecosystem, USB 2.0 OTG devices are referred to as Dual Role Ports (DRP). A DRP denotes a device capable of functioning as either a USB host or a USB device. In Type-C terminology, the USB host is termed the Downstream Connection Port (DFP), while the USB peripheral device is designated as the Upstream Connection Port (UFP).

To determine the DFP or UFP role, the DRP device must switch between UFP and DFP until the connection is established.

For reference, the following diagram illustrates the DRP model provided by the USB Type-C specification.

DRP Model

The DFP has a pull-up resistor (Rp), while the UFP has a pull-down resistor (Rd). The figure illustrates control of Rp and Rd on CC1/CC2 via switches. When Rp is selected for connection, the DRP device becomes the DFP (host) and supplies VBUS to the peripheral device. When a connection is made with the selected Rd, the DRP device becomes the UFP (USB generic device), monitoring VBUS to establish data connections and/or power supply circuits.

When two DRP-capable products connect, either may act as host or peripheral. For example, both a phone and tablet may support DRP. However, when connected, the phone becomes the peripheral while the tablet acts as host. The scenario where the phone becomes the tablet’s host and supplies VBUS to the tablet should not occur. In other words, the user’s phone should not charge the tablet.

For the above scenario, the Type-C specification provides selective paths for DRP connection and role detection, allowing devices to choose preferred settings for specific applications.

These option paths are called Try.SRC and Try.SNK. Utilizing these selective functions is crucial for portable devices. A tablet might want to use Try.SRC, enabling it to act as the host when connecting to other DRPs. Conversely, a phone might want to use Try.SNK, allowing it to become a peripheral device when connecting to other DRPs.

The diagram also shows the VCONN switch. VCONN’s purpose is to supply power to cables with active circuits. In Type-C, these cables are called active cables. VCONN is typically used to power USB 3.1 signal conditioning devices within the cable. Products supporting only USB 2.0 do not require VCONN support.