How is a USB-C to USB-C cable connected?

Aug 22, 2022

How is a USB-C to USB-C cable connected?

1. Function Definition of PINs of USB Type-C

Type-C is a form of USB interface. It is the only USB connector that does not care about the front side and back side when it is inserted. It supports USB standard charging, data transmission, video transmission, audio transmission, display output and other functions.

Another difference between USB Type-C and older standards is its dual-role capability. Both ends of each USB Type-C cable are mirrored, which means that the two connected devices must communicate with each other to determine whether they should exist as a host or a peripheral. The communication of the roles needs to be carried out separately for data and power, and this work should be carried out after the cable is connected.

The host port used for data communication is called Downstream Facing Port (DFP), and the peripheral port is called Upstream Facing Port (UFP). In terms of power supply, the power supply end is called the source end (Source), and the power consumption end is called the sink end (Sink). Some devices can have both the Dual Roles of Data (DRD) capability on the data and the Dual Roles of Power (DRP) capability on the power supply. The CC wire defines the role of the power supply during the connection between the two devices, communicating via the Type-C "Configuration Channel Pin CC"

2. How is a USB-C to USB-C cable connected?

The wiring diagram of the full-featured USB-C to USB-C GEN 2 Cable is as follows, provided by P-Shine Electronic Tech Ltd.

Status ① Unflipped direct connection

The image above shows the connection when the cable is Unflipped. From the socket on the left to the socket on the right, the RX1 pair is connected to the RX1 pair, the RX2 pair is connected to the RX2 pair; D+ is connected to D+, D- is connected to D-, SBU1 is connected to SBU2, and CC1 is connected to CC1. .

Sometimes the VCONNs at both ends of the cable do not need to be connected (B5 to B5). When the electronic mark (E-mark) chip is installed on the PCB of the USB-C connector, the B5 of the left plug and the B5 of the right plug need be connected to each other

State ② Flipped connection

When the plug and socket on the left remain the same, and the socket on the right also remains the same, but the plug on the right changes from one side to the other (USB-C supports front and back insertion), the USB-C connection flipped

In this case, from the socket on the left to the socket on the right, the RX1 pair is connected to the TX2 pair, the RX2 pair is connected to the TX1 pair, D+ is still connected to D+, D- is still connected to D-, SBU1 Connect to SBU1, SBU2 to SBU2, and CC1 connected to CC2 via the CC wire. Now, high-speed data is transmitted via RX1+/- and TX1+/- on the left to TX2+/- and RX2+/- on the right.

Both the left and right plugs can be flipped. It seems that there are four different connection methods in total, but there are actually only two, direct (flipping both ends at the same time is equivalent to direct) and one-sided flipped.

Therefore, you can see four pairs of high-speed signal pairs in the 3.1 cable of USB-C to USB-C Cable, but only two pairs are working at the same time, when one-sided plug fliped, the other two free signal pairs may replace the original working pairs. Or as the host and peripheral roles for power supply or data transfer change, signal pairs are constantly toggled.

In the USB 3.1 system, the RX/TX data pairs need to be configured for each possible connection state using a multiplexer so that correct communication can be formed. The figure below shows the routing possibilities of data pairs between USB Type-C ports, the orientation of the plug and socket can be known by measuring the status of CC1/CC2 on each terminal, the CC logic controller can then complete the routing configuration of the multiplexer, either in the multiplexer or in the USB chipset.