Understanding USB (Universal Serial Bus): Architecture, Connectors and Protocols

USB, or Universal Serial Bus, is a widely adopted industry standard that defines cables, connectors, and communication protocols for connection, communication, and power supply between computers and electronic devices. USB has become a ubiquitous interface for connecting a wide variety of peripherals and gadgets to computers, laptops, and other host devices.

USB has evolved through several versions, each introducing improvements in terms of data transfer speeds, power delivery capabilities, and other features. The USB versions include USB 1.0/1.1, USB 2.0, USB 3.0, USB 3.1 Gen 1, USB 3.1 Gen 2, USB 3.2, and USB 4.0.

USB uses a set of communication protocols to define how data is transferred between devices. It includes low-level protocols for data transfer, enumeration, and power management. The USB protocol is crucial for maintaining compatibility and ensuring efficient communication.

Following are the features and benefits of the USB interface:

• Universal Compatibility: USB is widely adopted across devices and operating systems, ensuring seamless connectivity.
• Plug and Play: USB supports instant device recognition and configuration without the need for restarting the computer.
• Hot Swapping: USB allows devices to be connected or disconnected without restarting the system, enhancing convenience.
• Power Supply: USB provides power to connected devices, eliminating the need for separate power adapters for many peripherals.
• Data Transfer Speeds: USB offers increasing data transfer speeds with each version, suitable for a broad range of applications.
• Versatility with USB Hubs: USB hubs expand available ports, simplifying organization and reducing cable clutter.
• Various Form Factors: USB supports different connector types, accommodating a wide array of device designs and applications.
• Device Enumeration: USB uses a standardized protocol for identifying and communicating with connected devices.
• Standardization and Interoperability: USB is a standardized technology, ensuring interoperability and compatibility across devices.

USB Architecture

USB architecture consists of several key elements, each serving specific functions in the data transfer process. Architecture follows tree topology and hence multiple I/O devices can be connected to the computer through USB as shown in the figure.

Every I/O device will make a point-to-point connection to transmit data through the serial transmission format. The Hub within the architecture is the connecting point between both the I/O devices as well as the computer. The root hub in this architecture is used to connect the whole structure to the hosting computer.

USB Connectors and Cables

USB connectors are physical ports that allow devices to be connected to a computer or other host devices. The most common types of USB connectors are Type-A, Type-B, Mini-USB, Micro-USB, and USB Type-C.

USB cables connect devices to each other through USB connectors. The cable itself consists of wires for data transfer, power delivery, and grounding. USB cables are also known as USB bus, pathway through which data travels between the host and connected devices.

USB Host

The USB host is typically a computer or a device that initiates and controls communication on the USB bus. It provides power and manages the data exchange with connected devices.

USB Device

USB devices are peripherals or gadgets that connect to a USB host to exchange data or receive power. Examples include keyboards, mice, printers, external hard drives, and smartphones.

USB Hubs

USB hubs allow multiple USB devices to be connected to a single USB port on a host device. They act as expanders, providing additional ports for connecting more peripherals.

USB Endpoints

USB endpoints are specific addresses within a USB device where data is sent or received. Each device can have multiple endpoints for various purposes, such as control, bulk, isochronous, and interrupt transfers.

USB Classes

USB classes define the functionality of a device and its driver requirements. Common classes include Human Interface Device (HID) for keyboards and mice, Mass Storage Class (MSC) for storage devices, and Audio Class for audio peripherals.

USB Power Delivery (PD)

USB PD is a specification that allows devices to negotiate and deliver higher power levels for charging and powering more demanding peripherals. USB PD is commonly associated with USB Type-C connectors.

USB On-The-Go (OTG)

USB OTG enables devices to act as both hosts and peripherals, allowing for direct communication between them without the need for a host computer. This is often used in mobile devices like smartphones and tablets.

Conclusion

In summary, USB (Universal Serial Bus) architecture provides a standardized and versatile interface for connecting devices across various platforms. With benefits like universal compatibility, plug-and-play functionality, hot-swapping support, and increasing data transfer speeds through evolving versions, USB simplifies connectivity, enhances user convenience, and accommodates a wide range of peripherals.