From personal computers and smartphones to external storage devices and various peripherals, USB is the most commonly used and versatile interface for connecting modern digital devices. It remains a convenient solution in the field of embedded systems, supporting a wide range of applications, including communication with data loggers and industrial controllers, firmware updates for medical devices and IoT devices, and the connection of peripherals in embedded Linux systems.
Today, mastering USB technology has become an essential foundational skill for embedded system design. This article provides a comprehensive overview of USB technology, covering everything from its historical development to the fundamentals of embedded development.
The Background of the USB's Development
USB (Universal Serial Bus) is now widely used for charging, data communication, and video transmission between personal computers and various electronic devices. Before 1996, connecting peripheral devices to personal computers required the use of various proprietary communication interfaces (PS/2, RS-232C, IEEE 1284, SCSI, IEEE 1394/FireWire, etc.). Each connected device required its own dedicated cable, and the setup process was extremely cumbersome.
Given this situation, there was a strong desire to simplify connections between personal computers and peripheral devices. Companies such as Intel and Microsoft took the lead in establishing a standards organization (USB-IF: USB Implementers Forum), which developed the USB 1.0 standard in 1996.
The original concept behind USB was to provide a unified standard that would allow various devices to connect to a single interface, enabling plug-and-play functionality—meaning devices could be plugged in or unplugged at any time while the system was powered on and used immediately—and allowing power to be supplied from the PC (bus-powered functionality). Subsequently, improvements to the USB 1.1 specification and Windows’ support for USB further enhanced its convenience, leading to rapid adoption.
Another key factor in USB’s widespread adoption was its royalty-free nature and the testing and certification system established to ensure communication quality. Subsequently, to meet growing demand, USB 2.0 (USB High-Speed), which supported high-speed communication, was introduced, and support in Windows 2000 and Windows XP further accelerated its adoption.