USB is a universal interface with a very successful design. It has grown by leaps and bounds in terms of protocols, physical interfaces, and additional functions. However, the official description of USB IF is a bit confusing. We will briefly explain the common interfaces.
There are many physical forms of USB interfaces, and we will not talk about rare or non-standard interfaces this time. This time we will mainly explain several common USB interfaces.
Physical Interface
USB Type-A
USB Type-A can also be called USB-A. I believe everyone is familiar with this interface. Until now, many PCs, PC peripherals, mobile phone chargers, etc. still use this interface. It is the most popular USB interface. USB-A is also divided into male and female sockets. The A end of the common USB-A data cable is the male socket, and the one on the charger is the female socket. There is no need to say more about this.
The structure of USB Type-A
The USB-A male connector has four notches on the top and bottom, which work together with the four protruding springs on the female connector to fix it. Therefore, there will be obvious scratching tracks on the USB-A male connector after repeated plugging and unplugging.
MicroUSB
USB-A is relatively large, which is not friendly to some portable or small devices. MicroUSB was born out of demand. The pin definition of MicroUSB is similar to that of various USBs, but there is one more pin for ID blank design. As mentioned earlier, MicroUSB is more used in some mobile phones (currently fully switched to USB-C interface) and various types of USB small devices (such as USB fans). Due to the low cost of MicroUSB, a large number of USB devices with low unit prices still choose this USB interface.
MicroUSB structure
MicroUSB uses two protruding small snaps to snap into the hollow position on the mother socket. Since the snap is in a spring-like form, the snap will return to a smaller and smaller amplitude after repeated plugging and unplugging, and the fixing performance will become worse and worse. In the end, the interface will not be able to be clamped, resulting in poor contact or even the interface coming out.
USB-A / MicroUSB high-speed interface
Since USB-A and MicroUSB were not designed with high-speed data transmission in mind when they were first introduced, the original hardware design could not meet this requirement when USB 3.0 (now renamed USB 3.2 Gen 1, and this term is used in the following description) was launched. Finally, USB IF launched a new USB-A design, adding a set of 4 lines of SSTX/SSRX for high-speed data transmission. And a GND was added for shielding. So far, USB-A can also perform high-speed data transmission.
On the other hand, the interface design of MicroUSB is not as spacious as USB-A, and more pins cannot be stuffed inside. At that time, there was no USB-C interface. In order to allow small USB devices to support the transmission speed of USB 3.2, the design structure of MicroUSB needs to be changed. USB IF decided to add a structural design to the original MicroUSB side and add 5 pins inside (the pin definition is consistent with USB 3.2 Type-A). So as to support the transmission speed of USB 3.2 Gen 2. Currently, the transmission interface of mobile hard disk accounts for the majority.
USB Type-C
USB Type-C, also known as USB-C. It is the latest physical interface in the current USB interface. Although it is not as small as MicroUSB, it is more functional and performant than MicroUSB. It also adds the function of blind plugging in both directions, which is more user-friendly. The fact that smartphones have begun to phase out MicroUSB also proves the power of USB-C design. The design of USB-C takes into account many future development directions, and various performance improvements have also strengthened some functional content. As a result, it has increased from only 4-10 pins in the past USB to a maximum of 24 pins (the full pin of the male connector is 22 pins). In order to unify all devices, the design of USB-C is very advanced and is currently the USB interface with the strongest performance and functions.
Briefly summarize the characteristics of USB-C:
1 - The base design current is 3A. By matching the USB PD protocol, the power supply performance can reach 100W;
2 - The positive and negative blind plug design is more user-friendly;
3 - The transmission speed is up to 40Gbps (only ThunderBolt3);
4 - Support DP, which can provide high-definition video and audio signal output for the display;
5 - Different functions can be realized through the selection of Pin / EMaker.
Pin analysis:
4 groups of VBUS (occupying 4 pins) GND (occupying 4 pins) - Since the original intention of USB IF to design USB-C was to solve the problem of all devices with one interface, the charging needs of some portable devices other than smartphones have long been considered. It supports power output up to 100W in conjunction with the USB PD protocol. Because the PD function output is up to 5A, the 1-pin VBUS in the past physical interface is not suitable for transmitting high power. Therefore, the USB-C interface is increased to 4-pin VBUS to enable it to transmit a larger current, and in terms of cable design. The cable body still has only one VBus for power supply (but it is much thicker).
2 groups of SSTX and SSRX (occupying 8 pins) - USB-C already supports high-speed data transmission of USB in its initial design, and compared with the traditional USB interface, it has one more SSTX and one SSRX. Two SSTX and SSRX form a full-duplex differential signal. SSTX / SSRX on USB-C can be used as the definition of USB 3.2&4, PCI-E (Thunderbolt 3&4, USB 4), Display Port (i.e. DP ALT Mode, USB IF part is only used in USB 3.X, USB 4 working principle has changed).
In the latest USB 3.2 Gen 2 specification, 2 groups of SSTX and SSRX can be used for simultaneous transmission (4 groups in total), making its transmission speed up to 20Gbps, and under ThunderBolt 3, it can be defined as PCI-E to 40Gbps. This is a speed that USB-A and MicroUSB 3.0 cannot reach. Because USB-C can transmit DP, USB monitors are the biggest beneficiaries.
D+/D- (the female socket is designed to occupy two groups of 4Pin, and the male socket has only one group on one side, i.e. 2Pin, and the remaining 2Pin is left floating) - D+/D- Needless to say, the USB 2.0 transmission that has been used to this day relies on it. Since only one set is needed and it can be plugged in either direction, the male socket is only designed for one side.
CC / VCONN (2 sets, 1 on each side, 2 pins in total) - CC Pin is one of the newly defined pins for USB-C, mainly responsible for protocol communication. VCONN is also one of the newly added pins, mainly for powering the EMarker in USB-C.
SBU (2 sets, 1 on each side, 2 pins in total) - A newly added pin on USB-C. SBU will be used in Alternate Mode and Audio Adapter Accessory Mode. For example, in DP Alt Mode, SBU will be used for AUX audio transmission.
Considering the significant improvement in the performance and functions of USB-C, the requirements for cables will also be relatively improved. But the question is, how to judge the quality of this cable? For this reason, USB IF added EMarker chips (similar to the chips on Apple's Lightning interface) to define various working modes. At present, this rule only applies to USB-C to C cables. A to C cables are only limited by length and current.
There is only one case where USB-C to C cables do not need to add EMarker, that is, cables running USB 2.0+3A current or less. This type of cable is usually used for some mobile phones and laptops within 60W. The relative price is also relatively cheap. Do you want to support USB 3.2 or 5A high current? Then you must add EMarker chips. There are also many types of EMarker chips, and the specific application scenario depends on what the data cable is used for, and the chip is not cheap.
P.S: USB IF calls this interface USB Type-C or USB-C. All expressions that do not include USB and express it as a Type-C interface are wrong (and very low-level errors). What does Type-C mean? I believe you all understand it without translation, right?
There are many types of USB-C. At the same level, the reliability of the one-piece USB-C head is higher than that of the stamped and riveted head. The riveted head has an obvious rivet line on one side, which can be observed from the product picture. At present, high-quality data cables basically use one-piece molded heads, but a few stamped and riveted heads have very good craftsmanship. You can only say that you get what you pay for. Of course, the reliability of the abnormal specifications of Apple in the picture above has surpassed many manufacturers, and the price is also very scary.
Transmission interface version
Confusing naming
In order to make it easier for consumers to understand the performance of each USB version, USB IF has specially reorganized a new naming method. As a result, the same specification of USB interface has several names. For example, USB 3.0 has several names. USB 3.0 / USB 3.1 Gen 1 / USB 3.2 Gen 1 / USB 3.2 Gen 1×1. It doesn’t matter if you don’t understand it, just remember the transmission speed of each version.
However, in some official USB IF documents on LOGO usage guidelines, the USB 3.2 Gen 2×2 LOGO has not yet been designed. Definitions such as SuperSpeed+ are not used for marketing, but many media seem to use the terminology of technical documents to spread it? It seems that no one has taken the official definition seriously.
USB 2.0 Brief Analysis
Since USB 1.0 / 1.1 is rarely seen on current devices, let's briefly talk about the common USB 2.0. USB 2.0 has three specifications: Low-Speed (USB 1.0, Basic-Speed in the market), Full-Speed (USB 1.1, Basic-Speed in the market), and High-Speed (Hi-Speed in the market). High-Speed is the highest transmission specification of USB 2.0, up to 480Mbps, which is 60MB/s. Although it is 60MB/s, in actual use, about 30-40MB/s is already the limit. With hard disks reaching T level and a 1080P movie reaching several GB, this transmission rate is really not enough.
USB 3.2 Brief Analysis
The biggest feature of the latest USB 3.2 is that it realizes dual-channel transmission function, thus achieving 20Gbps high-speed transmission. Following USB 3.0/3.1, the USB 3.2 standard specification was also released in September 2017. According to the USB IF's practice, the entire USB 3.0/3.1 family was upgraded to USB 3.2.
The previous specification can only use one set of SSTX and SSRX, and the maximum speed can only reach 10Gbps. USB3.2 uses two sets of SSTX and SSRX at the same time, and the maximum speed is increased to 20Gbps. Since USB-A, USB-B, and MicroUSB in the past only have one set of SSTX and SSRX, USB 3.2 Gen 1×2 and USB 3.2 Gen 2×2 can only be supported by USB-C.
What is the difference between USB 3.0 / 3.1 / 3.2?
USB 3.2 Gen 1x1: uses 8b/10b encoding, single-channel 5Gbps data rate; (actually renamed USB3.0 / USB3.1 Gen 1, the marketing name is USB 3.2 Gen 1 / SuperSpeed USB)
USB 3.2 Gen 1x2: uses 8b/10b encoding, dual-channel 10Gbps data rate; (USB3.1 Gen 1 dual-channel mode, this mode is not in the official language usage guide. Is it a backup mode?)
USB 3.2 Gen 2x1: uses 128b/132b encoding, compared with 8b/10b encoding 20% loss reduced to 3%, single-channel 10Gbps data rate; (actually renamed USB3.1 Gen 2, the marketing name is USB 3.2 Gen 2 / SuperSpeed USB 10Gbps)
USB 3.2 Gen 2x2: Using 128b/132b encoding, the loss is reduced to 3% compared to 8b/10b encoding, and the data rate of dual channels is 20Gbps.
USB 3.2 is compatible with existing cables and supports seamless switching between SSTX and SSRX. However, there are very few devices that support USB 3.2, and the accessories that can be matched with it are also very expensive. (For example, a USB-C to C data cable that supports USB 3.2 Gen 2 costs dozens of yuan, and a data cable that perfectly supports data transmission and 5A current is even more expensive).
Love and hate, the conflict between USB 3.2 and WIFI and mobile network
USB 3.2 and mobile phone WIFI and signals all have frequency band conflicts. To reduce the impact of USB high-speed transmission
1: Strengthen the shielding of wires and interfaces
2: Increase the distance between each other
3: Reduce the transmission speed of USB 3.2
4: Change the wireless frequency band to 5GHz
Therefore, many mobile phones still use USB 2.0 in daily use. Some mobile phones use USB 3.2 as an optional option for users to choose, strengthen the materials of wires and mobile phones, or reduce the speed limit to reduce noise. The reason why the USB 3.2 of the smart router is close to the antenna is that the USB 3.2 compatibility mode is also added, and the way is to reduce the speed of USB 3.2.
Summary
So, this is the brief analysis of the various versions of USB. USB-C actually adds a very important new technology: USB Power Delivery. This technology is the key to USB supporting up to 100W output. Finally, let's summarize the highlights of this article:
1: Specifications, marketing terms and developer terms are related but independent of each other, so one speed specification has multiple terms;
2: The marketing terms for Low-Speed and Full-Speed are unified as Basic-Speed USB;
3: The marketing terms for USB 3.2 5Gbps / 10Gbps / 20Gbps are SuperSpeed USB / SuperSpeed USB 10Gbps / SuperSpeed USB 20Gbps respectively;
4: USB-C is the future of great unification, and its hardware design has comprehensively surpassed previous USB interfaces;
5: Power supply performance has nothing to do with the version number, but only with the interface and protocol;
6: USB 3.0 / 3.1 has been renamed, and not many people know about the name change;
7: It will take time for USB 3.2 20Gbps to become popular, and there are very few devices that support full 20Gbps.