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USB Type-C® Alternate Mode

Last modified by Microchip on 2023/11/09 08:55

A central feature of USB Type-C® Power Delivery (PD) protocol is the ability to activate Alternate mode.

Alternate mode allows some of the pins on a Type-C connector to be reconfigured to support other protocols.

Reconfigurable Pins on a Full Featured Cable diagram

Reconfigurable Pins on a Direct Connect Application diagram

Using the PD protocol, the Downstream Facing Port (DFP) begins the negotiation with the Upstream Facing Port (UFP) to enter Alternate mode.

  • The DFP queries the UFP for a list of supported modes.
  • The UFP responds with a report of the available modes the UFP can support.
  • The DFP selects a mode, then directs the UFP to reconfigure the pins and enter Alternate mode.
  • Both the UFP and DFP enter Alternate mode.

Alternate Mode Example

A user-designed or industry-standard protocol can be run using Alternate mode. A common use of Alternate mode is a video monitor.

  • The UFP (Monitor) and the DFP (Portable Workstation) are connected with a Type-C cable
  • The DFP enumerates
  • Using the Power Delivery Protocol, both the UFP and DFP enter Alternate mode and set the interface to a graphics interface

Active Signals During Enumeration

Active Signals During Enumeration diagram

Active Signals for Alternate Mode Graphics Client

Active Signals for Alternate Mode Graphics Client diagram

Active Signals for Vendor Specific Device

Active Signals for Vendor Specific Device diagram

Information

Note:

In Alternate mode, the USB signals are still active allowing the UFP to re-enumerate if needed.

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