**Current USB Type-C Release Version**

The latest USB Type-C release version is 2.0, published by the USB-IF in August 2019. Compared to the currently mainstream USB Type-C Specification Release 1.3 and 1.4 versions, the 2.0 version primarily refines and clarifies Type-C functionality, definitions, applicable interfaces, and protocols. It essentially declares that USB Type-C has completely broken free from its subordinate relationship with USB and now stands on its own. A significant portion of the document emphasizes its capability to be compatible with various protocols and specifications. The USB Type-C interface has a very wide range of applications, capable of transmitting DP, USB, PCIe, audio, and other signals – it is no longer purely used for transmitting USB signals. This is an important area to focus on. Let's take a look at the specification interpretation for this version.

**Related Protocol Source**

The latest protocol, "USB Type-C Specification Release 2.0.pdf," is currently available for download on the USB official website (www.usb.org), with the latest version dated August 2019.

The main content of this protocol defines the USB Type-C plug dimensions, pin definitions, and related power delivery, audio transmission, receptacles, and cables. It specifically adds clarifications on the division of responsibilities between the USB 3.2 protocol and the PD (Power Delivery) protocol.

**The Most Important Difference: Detailed Charging Clarifications**

USB Type-C sources (hosts or downstream hub ports) can implement higher source current on VBUS to enable faster charging for mobile or powered devices that require more current than specified in the USB 3.2 specification. All USB hosts and hub ports use the CC (Configuration Channel) pins to set the currently available current level.

USB PD (Power Delivery) power supply capabilities for each mode are shown in the table below:

*Table: USB PD Power Profiles (omitted in text)*

**USB PD (Power Delivery)**

As specified, the PD protocol can switch the charging source/sink, switch data DFP (Downstream Facing Port) and UFP (Upstream Facing Port), and also switch who provides the cable voltage VCONN.

**Terminology Explanation**

In USB 2.0 ports, USB defines three roles based on data transmission direction: HOST, Device, and OTG (On-The-Go). OTG can act as either Host or Device. In Type-C, there are similar definitions.

*   **DFP (Downstream Facing Port):** This can be understood as a Host or Hub. DFP provides VBUS and VCONN and can receive data. In the protocol specification, DFP specifically refers to downstream data transmission. Broadly, it refers to devices that provide downstream data and external power.

*   **UFP (Upstream Facing Port):** This can be understood as a Device. UFP draws power from VBUS and can provide data. Typical devices are USB flash drives and external hard drives.

*   **DRP (Dual Role Port):** This is similar to the previous OTG. DRP can act as either DFP (Host) or UFP (Device) and can dynamically switch between them. A typical DRP device is a laptop. The initial role upon connection is determined by the Port's Power Role (see later introduction); it can later be changed through a switch process (if the USB PD protocol is supported).

Regarding USB PORT power supply (or power reception), USB Type-C divides ports into Source and Sink.

*   **Source:** Supplies power through VBUS or VCONN.

*   **Sink:** Receives power through VBUS or VCONN.

*   **DRP (Dual-Role-Power):** Can act as either Source or Sink. The final role is determined by the configuration after device connection.

**Source and Sink Connection Process**

Under general USB conditions for Source and Sink, the typical interface configuration flow is as follows:

1.  First, detect a valid connection between ports (including determining cable orientation, Source/Sink, and DFP/UFP relationships).

2.  Then, detect the cable's capabilities.

3.  Then, turn on USB power (negotiate USB power delivery, select power supply mode, battery charging, etc.).

**Interaction Between Role Ports: Source to Sink**

*Brief description:* After the Source and Sink are connected via Type-C, the Source detects the Sink's pull-down resistor Rd through the CC pin, confirming a Sink connection. The Source then turns on VBUS and VCONN (on the other CC pin), establishing a connection. The Source can control the voltage value on vRd by adjusting the size of the pull-up resistor Rp. The Sink detects the vRd voltage value to determine how much current it can draw from VBUS.

**Interaction Between Role Ports: Source to Sink Connection Detection**

*Description:* When not connected, the Source detects that both CC pins are at a high level, and the Sink detects that both CC pins are at a low level. After connection, a voltage divider is formed, and the voltage is at an intermediate level. The resistance value of Rp indicates the power level the Source can provide.

**Interaction Between Role Ports: Source to DRP**

*Description:* DRP continuously switches its connection between pull-up resistor Rp and pull-down resistor Rd before establishing a connection. After the Source and DRP are connected via Type-C, when the DRP is connected to Rd, the Source detects Rd through the CC pin, then turns on VBUS and VCONN. The DRP detects the Source's Rp, waits for the Source to turn on VBUS, then confirms the transition to Sink and formally establishes the connection. In addition to Source to Sink, when a Source connects to a DRP, the DRP adapts to the Sink role. When a Sink connects to a DRP, the DRP adapts to the Source role. Source-to-Source and Sink-to-Sink connections will not be successful.

**Interaction Between Role Ports: DRP to DRP**

This scenario is the most complex because DRPs can be further divided into three roles: Normal DRP, DRP Try Source, and DRP Try Sink. Some DRPs have a preferred role in DRP-to-DRP connections. For example, both a laptop and a phone are DRPs, but the laptop might be set as Try Source because it has a larger battery capacity. Connecting a laptop and a phone is best done with the laptop as the Source to charge the phone, not the other way around. However, when connecting a laptop to a wall charger, the laptop acts as a Sink.

*Description:* In the Type-C specification, the behavior when two DRPs are connected mentions three cases. Case 2 and Case 3 involve situations where one DRP is Try Source or Try Sink, which are relatively complex.

When a formal connection is not yet established, both DRPs are continuously switching their pull-up and pull-down resistors. At a certain moment, DRP1 might have the pull-up resistor and DRP2 the pull-down resistor, and the situation then proceeds similarly to the Source-to-Sink case. Because the states of the two DRPs are constantly switching, their states at the moment of connection determine the resulting master-slave relationship. Of course, if at some moment both DRPs are pull-up or both are pull-down, the connection attempt will fail, and the DRPs will re-enter the continuous switching state, waiting for the next connection attempt.

Would there be an extreme situation where two DRPs switch states too synchronously, always both pull-up or both pull-down, preventing them from ever connecting? This relates to the DRP switching period issue. Refer to the specification description for details.

*Description:* The SPEC defines a complete swap cycle for DRP switching between Source and Sink as tDRP, where dcSRC.DRP is the percentage of the entire cycle that the DRP acts as a Source. The SPEC explicitly states that the clock used to control this cycle and percentage must not come from a highly accurate clock source, such as a crystal oscillator or ceramic resonator, in order to minimize the possibility of infinite failed pairing attempts between two DRPs. The upper and lower limits for each cycle are also very generous, so in practice, the cycles of different DRPs will vary, and the situation where two DRPs switch cycles perfectly synchronously, leading to infinite pairing failures, will not occur. The conclusion is that the master-slave result of connecting two DRPs is random.