USB Type-C Working principle of depth analysis


   A bunch of people are talking about USB Type-C since Apple released the new MacBook. I come from the hardware point of view under this USB Type-C, the way to solve the problem.


Small size, support positive and negative plug, fast (10Gb). This is small for the previous USB interface on the computer said that the actual relatively microUSB on the android machine is also a big point:

USB Type-C:8.3mmx2.5mm



So, I do not see the benefits of USB Type-C on a handheld device in terms of size. The speed, can only see the video transmission is needed.

Pin definition

It can be seen that the data transmission mainly has two differential signals of TX / RX, CC1 and CC2 are two key pins, which have many functions:

•Probe connection, distinguish between positive and negative, DFP and UFP distinction, that is, master-slave

• Configure Vbus, USB Type-C and USB Power Delivery two modes

•Vconn configuration, when there is a chip in the cable, a cc signal transmission, a cc into a power Vconn

• Configure other modes, such as when audio accessories, dp, pcie

There are 4 power and ground, which is why you can support the reason to 100W.

Do not look at the USB Type-C seems to support up to 20V / 5A, in fact this requires USB PD, and support for USB PD requires additional pd chip, so do not think it is USB Type-C interface can support up to 20V / 5A.

Of course, there should be integrated chips later.

Auxiliary signals sub1 and sub2 (Side band use), only used in certain transmission modes.

d + and d- are compatible with pre-USB standards.

Here to talk about, USB3.0 only a group of RX / TX, the speed is 5Gb, USB Type-C in order to ensure both positive and negative can be used to plug in two groups, but in fact the data transmission or only a set of RX / TX, Speed has reached 10Gb. If the back of the upgrade agreement, the two groups are the same words and DisplayPort 20Gb.

work process

The DFP (Downstream Facing Port) is the master and the UFP (Upstream Facing Port) is the slave. In addition to DFP, UFP, there is a DRP (Dual Role port), DRP can do DFP can do UFP. When the DPR receives the UFP, the DRP is converted to DFP. When DRP is connected to DFP, DRP is converted to UFP. Two DRP together, this time is either DFP, the other party is UFP.

The pull-up resistor Rp on the CC pin of DFP and the pull-down resistor Rd on UFP. VBUS for DFP is not output when it is not connected. After the connection, the CC pin is connected, the DFP CC pin will detect the UFP pull-down resistor Rd, indicating that the connection is made and DFP turns on the Vbus power switch to output power to the UFP. Which CC pin (CC1, CC2) to detect the pull-down resistor to determine the direction of the interface to insert, by the way switch RX / TX。

Resistance Rd = 5.1k, the resistance Rp is indefinite value, according to the previous figure to see the USB Type-C has several power supply modes, depending on what to identify? Rp value depends on the value of Rp is not the same, CC pin detection The voltage is not the same, and then to control what DFP side of the power supply mode.

It should be noted that the picture above draw two CCs, in fact there is only one cc line in the chip without the cable.

Instead of two cc wires, the chip-containing cable is a cc, a vconn, which is used to power the chip in the cable (3.3V or 5V). There is no pulldown resistor Rd on the cc side, instead Pull-down resistor Ra, 800-1200 ohms.

When the CC pin two are connected to the pull-down resistor <= Ra, DFP into the audio accessories mode, left and right channels, mic are all, as shown above.

USB Type-C和DisplayPort,PCIE

USB PD is BMC encoded signal, and the previous USB is FSK, so there is not compatible, do not know whether there is currently available on the market to convert the product.

USB PD is transmitted on the CC pin, PD has a VDM (Vendor defined message) function, defines the device ID, and reads devices supporting DP or PCIe. DFP enters alternate mode.

If DFP recognizes the device as DP, it switches the MUX / Configuration Switch to change the Type-C USB3.1 signal pin to transmit the DP signal. AUX Assisted by Type-C SBU1, SUB2. HPD is the detection of foot, and CC similar, so shared.

The DP lane 0-3 four groups of differential signals, Type-C has RX / TX1-2 is also four sets of differential signals, so no problem completely replaced. And in the DP protocol alternative mode, USB signals and DP signals can be simultaneously transmitted, RX / TX1 USB data transmission, RX / TX2 replaced lane0,1 two sets of data transmission, this time can be supported to 4k.

If DFP recognizes the device as a DP, it switches the MUX / Configuration Switch to change the Type-C USB3.1 signal pin to transmit the PCIe signal. Similarly, PCIe uses RX / TX2 and SBU1, SUB2 to transmit data and RX / TX1 to transmit USB data.

The advantage is that an interface uses two devices at the same time, of course, the conversion line can be done without any chip.


USB Type-C has ended a long time USB plug to plug the shortcomings, saving people a lot of time, for a second direction at least 2s, plug the world once a billion people USB, 50% probability of error, a total of time-consuming 277,000 hours, about 31 years, horrible.

An interface to get the three kinds of audio and video data, the size is still small. It is foreseeable that after Android can be changed to USB Type-C interface, if only need USB2.0, only need to redo the cable, no chips, the cost can be completely negligible.

As for the Thunderbolt, lightning, how to still be how it, after all, flowers bloom is a colorful world.

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