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GENERATORS, BACKUP POWER & BATTERIES


"upstream" controller typically being internal to a desktop PC or laptop. A maximum of 127 devices can attach to a single controller through several external hubs. The connected peripherals are categorised according to class types (HMI, media streaming, etc.). Each device, a keyboard, for example, is uniquely identified with an address and, typically, three logical endpoint channels. Each endpoint has a specific function, and the specification accommodates up to 32 endpoints in a single device - see Figure 4. Communication between the host controller


and device takes place via bidirectional pipes, either control or data. The pipe functions depend on the device class, which usually defines the data transfer types. There are four types of data transfer: control, interrupt, bulk, and isochronous. Figure 5 illustrates the attributes of each data


Figure 2 - USB evolution from 12 Mbits/s to 20 Gbits/s (Source: Mouser)


consumer audiences, each speed specification had a non-technical name. The 12Mbit/s standard became known as USB Full Speed and the 1.5Mbits/s as USB Low Speed. The USB-IF followed this approach with USB 2.0 in 2000, with a 480Mbit/s standard known as High Speed, and in 2008, USB 3.0, capable of up to 5Gbit/s, known as SuperSpeed USB - see Figure 2. In 2013, USB 3.1 SuperSpeed+ delivered up to 10Gbit/s, and USB 3.2 in 2017 introduced a dual- lane approach doubling the data rate to 20Gbit/s. In just over a decade, the USB transfer rates increased by 1666-fold, and USB adoption expanded rapidly. USB also survived several competing technologies during the period, such as Apple's faster but more complex to implement, Firewire. The USB 3.0 specification saw several data


rate iterations and, more significantly, the announcement of the USB-C connector type. The USB-C connector is notable for the broader


Figure 3 - the increase of USB power delivery capability from 2.5W to 100W permits powering of many more device types (Source: USB-IF)


range of devices it serves and that it doesn't matter which way it is inserted. USB-C has quickly established itself as a primary method of charging and powering portable devices, from smartphones to laptops. The power delivery capability has increased to match a conventional power adapter. Also, USB-C and USB 3.0 introduced a range of different voltage outputs, adding 9V, 12V, 15V, and 20V. Since the beginning, USB has strived to continue its initial goals. Cable lengths are kept relatively short, the intention being to connect devices in the same physical location as the host rather than stray into networking use cases. Also, the tree connection topology requires all communication to pass through the host controller. Devices cannot directly talk to each other.


USB ARCHITECTURE AND CONCEPTS The functional architecture of USB functions on a tiered-star host approach, with the root host


transfer type and lists an example use case for each. The device initialisation (enumeration) process


is instigated by connecting a USB device to a host controller. This step involves the host issuing a reset signal to the device and requesting the device's parameters to establish the device class and transfer speed. Once received, the host controller allocates a unique 7-bit address to the device, after which data transfer can commence. For a more in-depth technical explanation of the USB architecture and operation, the reader will find helpful resources on the USB-IF website. The Infineon (was Cypress) application note AN57294 also gives a detailed explanation of USB 2.0 operation.


CONTINUED EVOLUTION DELIVERS THE USB4 SPECIFICATION In late 2019, the USB-IF announced the USB4 specification. Building on the architecture of USB 2.0 and USB 3.4, the USB4 specification is primarily based on the Thunderbolt protocol. Data transfer up to 40Gbits/s using a two-lane


Continued on page 20... FACTORY&HANDLINGSOLUTIONS | NOVEMBER 2023 19


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