Application of USB-C Alternate Mode

Mon Jun 26 10:16:46 CST 2023

0_Type-C-Alternate-Mode-HornmicLink

Application of USB-C Alternate Mode

Introduction to USB-C

USB-C, the USB Type-C interface, is the most likely interface launched by the USB-IF to unify the world. Compared to traditional USB interfaces, USB-C has a slim structure, supports forward and reverse insertion, high power transmission, and supports optional mode (DisplayPort/Thunderbolt, etc.) output of outstanding quality features, and its size comparison is shown in the figure below.

1_USB-C-combines-all-in-one-Hornmic

The highly integrated nature of USB-C allows users to transfer data, video, and power on the same cable, streamlining the complexity of device use and making electronic devices more aesthetically pleasing and sophisticated, thus attracting much attention in the consumer electronics market.

The USB-PD protocol is a communication protocol that runs on the USB-C interface. Unlike traditional USB protocols, the USB-PD protocol is not usually used for data transfer, but only for setting the properties of the USB-C interface. Simply put, USB-C is the interface and USB-PD is used to establish specific data and power attributes including power capability, optional modes, etc.

1_VESA-DisplayPort-Alternate-Mode-on-USB-Type-C

What is the Alternate Mode of USB-C?

Alternate Mode is a mode that USB-C supports in addition to traditional USB data transfer - such as image data (DisplayPort) or Thunderbolt, etc. The USB Association issues a unique 16-bit USB standard code (SID) for each standard Alternate Mode The USB Association issues a unique 16-bit USB standard code (SID) for communication between master and slave devices for Alternate Mode support or not.

2_USB-Type-C-receptacle-pins-DP-Alt-Mode

DisplayPort (DP for short) is a digital video interface standard introduced by the Video Electronics Standards Association (VESA), and has received the first Alternate Mode standard code (0xFF01).

USB data and DP Alternate Mode data can be transmitted simultaneously. The two different data split the four pairs of high-speed differential signal lines of USB-C into two groups to transmit different data without interfering with each other.USBC also provides two signal lines Sideband Use (SBU) as a supplement for Alternate Mode, which are used to transmit low-speed data or configuration information, and are used in DP mode to pass the auxiliary channel ( AUX) signals in DP mode. (e.g. display information such as EDID in DP)

3_USB-Type-C-Connector-PHY-Switch-DisplayPort-Alternate-Mode

How to switch into Alternate Mode of USB-C?

A new USB class, Billboard (USB2.0 device), is proposed in USB-C. Its role is to enumerate when a device fails to enter Alternate Mode or when an unknown error occurs, so that the host can obtain the status of Alternate Mode. If the Billboard is not integrated in the peripheral devices that support Alternate Mode, the biggest impact is that the host can not effectively know the operating status of the device. Therefore, if the customer's product needs to support Alternate Mode, then the Billboard device must be added to the peripheral.

Necessary conditions to enter USB-CAlternate Mode:

1. The host supports USB Type-C, USB-PD (Power Delivery) protocol.

2. The host supports some Alternate Mode.

3. the peripheral supports USB-PD protocol.

4. the peripheral supports the corresponding Alternate Mode.

The initial state of peripheral and host connection is USB mode, after which several different situations will occur, which will be analyzed step by step below:

1. If the host does not support USB-PD protocol, after a certain waiting time, the peripheral will enumerate the Billboard device to notify the computer of the failure to enter Alternate Mode, as shown in the figure below.

4_failure-to-enter-Alternate-Mode-USB-C

2. The computer supports USB-PD protocol, but does not support the Alternate Mode selected by the peripheral, the peripheral will enumerate Billboard devices to notify the computer of the failure to enter Alternate Mode. Note that Windows 10 system currently supports Billboard device class, Windows 8 system needs to install the corresponding patch to support.

3. If the computer supports both USB-PD protocol and Alternate Mode of the peripheral, it will enter Alternate Mode according to the following procedure.

a) The computer sends the Discover Identity command.

The peripheral responds to this command and declares that it is an Alternate Mode Adapter (AMA) that supports Alternate Mode.

b) The computer sends the Discover SVIDs command to obtain all Alternate Modes supported by the peripheral.

The peripheral responds to this command and reports the type of Alternate Mode supported (e.g. DP mode is 0xFF01).

c) The computer sends the Discover Modes command to get the submodes supported by the peripheral under a standard vendor code.

The peripheral responds to this command and reports all supported submodes.

d) The computer selects to enter the appropriate mode (Enter Mode) based on the peripheral's settings and the computer's limitations.

The peripheral receives this command and responds with an ACK, exits USB mode, and enters the corresponding Alternate Mode.

The computer receives this response, exits USB mode, and enters the corresponding Alternate Mode.

This process can be summarized in the following diagram.

5_process -to-enter-Alternate-Mode-USB-C

Depending on the characteristics of USB-C, it can be made into different forms of extension devices that support Alternate Mode, as follows:

6_extension-devices-support-Alternate-Mode-USB-Hub-HornmicLink

Summary

USB-C inherits the advantages of the traditional USB interface while adding Alternate Mode, making this interface technology more open and inclusive. It is foreseeable that the sea of USB-C technology will become the mainstream of the market in the next few years, gradually replacing the traditional USB interface or DP interface. For the current market, the USB-CAlternate Mode conversion adapter will definitely be sought after by the majority of peripheral manufacturers as a transitional product, while personalized product form is the primary choice of each visionary company, using a programmable, highly integrated USB-C PD controller as the design platform will provide unlimited possibilities for companies to capture the market.



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By HornmicLink_Mia.J @230626 10:20