Since Apple released the new MacBook, a bunch of people have been talking about USB Type-C. Let me analyze this USB Type-C from a hardware perspective, by the way. Small size, support positive and negative insertion, fast speed (10Gb). This small is for the USB interface on the previous computer, but it is actually a bit larger than the microUSB on the android machine:


USB Type-C:8.3mmx2.5mm


And lightning: 7.5mmx2.5mm

So, I don't see the advantage of USB Type-C on handheld devices in terms of size. And the speed can only see if the video transmission is needed.

  pin definition


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

Detect connections, distinguish front and back, distinguish DFP and UFP, that is, master and slave

Configure Vbus, there are two modes of USB Type-C and USB Power Delivery

Configure Vconn, when there is a chip in the cable, one cc transmits the signal, and one cc becomes the power supply Vconn

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

There are 4 power supply and ground, which is why it can support up to 100W.


  Don't look at USB Type-C as if it can support up to 20V/5A. In fact, this requires USB PD, and supporting USB PD requires an additional pd chip, so don't think that the USB Type-C interface can support up to 20V/5A.

Of course, integrated chips should appear in the future.

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

d+ and d- are for compatibility with pre-USB standards.

  Let me talk about it here, USB3.0 has only one set of RX/TX, and the speed is 5Gb. USB Type-C uses two sets to ensure that both front and back can be inserted, but in fact, only one set of RX/TX is used for data transmission. The speed has reached 10Gb. If the protocol is upgraded later, the two groups will transmit the same 20Gb as DisplayPort.

  work process


In the picture above, DFP (Downstream Facing Port) is the master, and UFP (Upstream Facing Port) is the slave. In addition to DFP and UFP, there is also a DRP (Dual Role port), which can be used as DFP or UFP. When DPR receives UFP, DRP is converted to DFP. When DRP receives DFP, DRP is converted to UFP. When two DRPs are connected together, either one is DFP and the other is UFP.

There is a pull-up resistor Rp on the CC pin of the DFP, and a pull-down resistor Rd on the UFP. When not connected, the DFP's VBUS is no output. After the connection, the CC pin is connected, and the CC pin of the DFP will detect the pull-down resistor Rd of the UFP, indicating that it is connected, and the DFP will turn on the Vbus power switch and output power to the UFP. Which CC pin (CC1, CC2) detects the pull-down resistor determines the direction of the interface insertion, and switches RX/TX by the way.

The resistance Rd=5.1k, and the resistance Rp is an indeterminate value. According to the previous figure, we can see that there are several power supply modes for USB Type-C. How can we identify them? Depending on the value of Rp, the value of Rp is different, the voltage detected by the CC pin is different, and then it controls which power supply mode the DFP terminal executes.

  It should be noted that two CCs are drawn in the above picture, but there is actually only one CC wire in the cable without the chip.

The cable with the chip is not two cc lines, but one cc and one Vconn, which are used to power the chip in the cable (3.3V or 5V). At this time, there is no pull-down resistor Rd on the cc end, but Pull-down resistor Ra, 800-1200 ohms.


When both CC pins are connected to pull-down resistors<>

 USB Type-C和DisplayPort,PCIE

USB PD is a signal encoded by BMC, while the previous USB is FSK, so there is incompatibility. I don't know if there are any products that can be converted on the market.

The USB PD is transmitted on the CC pin. The PD has a VDM (Vendor defined message) function, which defines the device ID. When a device that supports DP or PCIe is read, the DFP enters the alternate mode.

If the DFP recognizes that the device is DP, it will switch the MUX/ConfiguraTIon Switch to change the Type-C USB3.1 signal pin to transmit the DP signal. AUX is transmitted by SBU1 and SUB2 of Type-C. HPD is a detection foot, similar to CC, so it is shared.

DP has four sets of differential signals from lane0-3, and Type-C has four sets of differential signals for RX/TX1-2, so it is no problem to completely replace it. Moreover, in the alternative mode in the DP protocol, USB signals and DP signals can be transmitted at the same time, RX/TX1 transmits USB data, RX/TX2 is replaced with lane0, 1 two groups of data transmission, which can support up to 4k at this time.

If the DFP recognizes that the device is DP, it will switch the MUX/ConfiguraTIon Switch to change the Type-C USB3.1 signal pin to transmit PCIe signal. Similarly, PCIe uses RX/TX2 and SBU1, SUB2 to transmit data, and RX/TX1 to transmit USB data.

The advantage of this is that one interface uses two devices at the same time. Of course, the conversion line can do it without any chips.


USB Type-C puts an end to the long-standing defect of USB plugging and unplugging, saving people a lot of time. Change the direction for at least 2 seconds. According to the world's 1 billion people plugging and unplugging USB once a day, there is a 50% probability of wrong plugging, which takes a total of time consuming. 277,000+ hours, about 31 years, which is horrible. One interface handles three kinds of audio and video data, and the volume is relatively small. It is foreseeable that the Android phone can be changed to the USB Type-C interface in the future. If only USB2.0 is needed, it is only necessary to redo the cable without the chip, and the cost can be completely ignored. As for Thunderbolt, lightning, what to do or what to do. A hundred flowers blooming is a colorful world.

Here, by the way, I will introduce the specific parameters of the Type-C connector of the connector leader Foxconn.

Foxconn connector main parameters

If you want to fully understand the detailed parameters, you can get the specification and sample test from the link below

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