Sat Nov 12 23:47:21 CST 2022
The USB Type-C connector has 24 pins.
- GND - 4 pcs
- Differential pairs - 4 Pairs
- VBUS - 4 pcs
- CC - 2 pcs
- SBU – 2 pcs
- Signal - 2 Pairs
RX=Rceive, the case of receiving packets, is the downlink traffic (Downlink).
TX=Transmit, the case of sending packets, is the uplink traffic (Uplink).
There are two sets of RX differential pairs and two sets of TX differential pairs.
One of these two RX pairs along with a TX pair could be used for the USB 3.0/USB 3.1 protocol. Since the connector is flippable, a multiplexer is required to correctly re-route the data on the employed differential pairs through the cable.
Note that a USB Type-C port could support USB 3.0/3.1 standards but the minimum feature set of USB Type-C doesn’t include USB 3.0/3.1. In such cases, the RX/TX pairs are not used by the USB 3.0/3.1 connectivity and could be used by other USB Type-C functionalities such as the Alternate Mode and the USB Power Delivery protocol. These functionalities may utilize even all of the available RX/TX differential pairs.
Typically, the USB 3.1 TX/RX crossover is done in the cable. This means that on the PCB you would normally wire the TX of a USB controller to the TX of a USB connector, and the RX of the USB controller to the RX of the connector. You would not cross the TX/RX over on the board.
These pins are the Channel Configuration pins. They perform a number of functions such as cable attachment and removal detection, receptacle/plug orientation detection, and current advertisement. These pins could be also used for the communications required by the Power Delivery and Alternate Mode.
Below figure shows how the CC1 and CC2 pins reveal the receptacle/plug orientation. In this figure, DFP stands for Downstream Facing Port which is the port acting as either the host in data transmission or the source for power. UFP denotes Upstream Facing Port which is the device connected to the host or the power consumer.
The DFP pulls up the CC1 and CC2 pins through the Rp resistors but the UFP pulls them down through Rd. If no cable is attached, the source sees a logic high at CC1 and CC2 pins. Connecting the USB Type-C cable creates a current path from 5-V supply to ground. Since there’s only one CC wire inside the USB Type-C cable, only one current path is formed. For example, in the upper graphic of upon Figure, the CC1 pin of the DFP is connected to the CC1 pin of the UFP. Hence, the DFP CC1 pin will have a voltage lower than 5 V but the DFP CC2 pin will be still at the logic high. Therefore, monitoring the voltage on the DFP CC1 and CC2 pins, we can determine cable attachment and its orientation.
In addition to the cable orientation, the Rp-Rd path is used as a way of communicating information about the source current capabilities. To this end, the power consumer (UFP) monitors the voltage on the CC line. When the voltage on the CC line has its lowest value (about 0.41 V), the source can provide the default USB power which is 500 mA and 900 mA for the USB 2.0 and USB 3.0 respectively. When the CC line voltage is about 0.92 V, the source can provide a current of 1.5 A. The highest CC line voltage which is about 1.68 V corresponds to the source current capability of 3 A.
Related knowledge:
>>> USB-C-Pins-explanation--1.html
>>>USB-C-Pins-explanation--3.html
By HornmicLink_Henry @221112 23:58