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2.3 Configuration Process
The USB Type-C receptacle, plug and cable solution incorporates a configuration process to detect a downstream facing port to upstream facing port (DFP-to-UFP) connection for VBUS management and host-to-device connected relationship determination.
The configuration process is used for the following:
DFP-to-UFP attach/detach detection
Plug orientation/cable twist detection
Initial DFP-to-UFP (host-to-device) and power relationships detection
USB Type-C VBUS current detection and usage
USB PD communication
Discovery and configuration of functional extensions
Two pins on the USB Type-C receptacle, CC1 and CC2, are used for this purpose. Within a standard USB Type-C cable, only a single CC pin position within each plug of the cable is connected through the cable.
2.3.1 DFP-to-UFP Attach/Detach Detection
Initially, DFP-to-UFP attach is detected by a host or hub port (DFP) when one of the CC pins at its USB Type-C receptacle senses a specified resistance to GND. Subsequently, DFP-to-UFP detach is detected when the CC pin that was terminated at its USB Type-C receptacle is no longer terminated to GND.
Power is not applied to the USB Type-C host or hub receptacle (VBUS or VCONN) until the DFP detects the presence of an attached device (UFP) port. When a DFP-to-UFP attach is detected, the DFP is expected to enable power to the receptacle and proceed to normal USB operation with the attached device. When a DFP-to-UFP detach is detected, the port sourcing VBUS removes power.
2.3.2 Plug Orientation/Cable Twist Detection
The USB Type-C plug can be inserted into a receptacle in either one of two orientations, therefore the CC pins enable a method for detecting plug orientation in order to determine which SuperSpeed USB data signal pairs are functionally connected through the cable. This allows for signal routing, if needed, within a DFP or UFP to be established for a successful connection.
2.3.3 Initial DFP-to-UFP (host-to-device) and Power Relationships Detection
Unlike existing USB Type-A and Type-B receptacles and plugs, the mechanical characteristics of the USB Type-C receptacle and plug do not inherently establish the relationship of USB host and device ports. The CC pins on the receptacle also serve to establish an initial DFP-to-UFP and power relationships prior to the normal USB enumeration process.
For the purpose of defining how the CC pins are used to establish the initial DFP-to-UFP relationship, the following port behavior modes are defined.
1. Host-only – for this mode, the port exclusively behaves as a DFP
2. Device-only – for this mode, the port exclusively behaves as a UFP
3. Dual-role – for this mode, the port can behave either as a DFP or UFP
The host-only and device-only ports behaviorally map to traditional USB host ports and USB device ports, respectively. When a host-only port is attached to a device-only port, the behavior from the user’s perspective follows the traditional USB host-to-device port model. However, the USB Type-C connector solution does not physically prevent host-to-host or device-to-device connections. In this case, the resulting host-to-host or device-to-device connection results in a safe but non-functional situation.
Initially, the DFP sources VBUS and the UFP sinks VBUS. USB PD may then be used to independently swap both the data and power roles of the ports.
USB hubs have two types of ports, a single UFP that is connected up to a host or another hub and one or more DFPs for connecting other devices.
A port that supports dual-role operation by being able to shift to the appropriate connected mode when attached to either a host-only or device-only port is a DRP. In the special case of a DRP being attached to another DRP, an initialization protocol across the CC pins is used to establish the initial host-to-device relationship, and in this case, the determination of which is DFP or UFP is random from the user’s perspective.
Two methods are defined to allow a USB Type-C DRP to functionally swap data roles, one managed using USB PD DR_Swap and the other emulating a disconnect/reconnect sequence (see Figure 4-16). As an alternative to role swapping, a USB Type-C DRP may provide useful functionality by when operating as a host, exposing a CDC/network (preferably TCP/IP) stack or when operating as a device, exposing a CDC/network interface. | 
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