Extending the reach of the USB specification - Embedded.com

Extending the reach of the USB specification


The Universal Serial Bus (USB), an industry standard developed in the mid-1990s, certainly lays to rest the stereotype that almost anything designed by a committee is doomed to disaster.

Originally designed as an 1.5 to 12 Megabits/second standard for connection of computer peripherals to personal computers, both to communicate and to supply electric power, USB has become commonplace on other devices as well, including smartphones, PDAs, MP3 players, video game consoles and even wearable IoT devices. The most recent implementation of the standard is the 10 gigabits/second USB 3.1 which in addition to the standard Type A and Type B connectors has given rise to the newest variation: Type-C .

USB in its various forms has replaced a variety of earlier interfaces, such as serial and parallel ports, as well as separate power chargers. The range of its applications are illustrated in the articles included in this week’s Tech Focus newsletter, of which my Editor's Top Picks are:

Incorporating USB battery charging protocols into an Android-based design
USB 3.0 vs USB 2.0: A quick reference summary for the busy engineer
The basics of USB device development using the Android framework

With USB 3.1’s new Type-C connector profile and its companion USB Power Delivery (“PD”) specification, the USB Implementers Forum hopes it will convince OEMs to do away with not only all of the variants, but displace as well other high speed protocols, such as the Mobile High Definition Link (MHDL), HDMI, PCI Express, and even Apple's Thunderbolt, at least in consumer electronics.

For one thing, USB 3.1 increases the data signaling rate to 10 Gbit/s in the USB 3.1 Gen2 mode, double that of USB 3.0 and reduces line encoding overhead to just 3%. The USB Type-C Specification 1.0 defines a new small reversible-plug connector for USB 3.1, half the size of the present one and can be used at both host and device side, replacing multiple type-B and type-A connectors and cables with a future-proof standard..

To make it even harder for OEMs to resist, the USB 3.1 Type-C cables are active, electronically marked cables, and will contain a chip with an ID function based on the configuration data channel and vendor-defined messages from the USB Power Delivery 2.0 specification. This will allow device and battery recharging from a host system up to 2 A at 5 V (10 W) in the standard reconfiguration, or optionally 3 A or 5 A at 20 V (60 W or 100 W).

Finally, to make USB 3.1 with Type-C absolutely irresistible, the specification defines an Alternate Mode that allows dedication of some of the physical wires in the type-C cable for direct device-to-host transmission of alternate data protocols, including HDMI, DisplayPort, and MHL, as well as other protocols such as PCI Express and even Base-T Ethernet.

Everything is not perfect, though. While the USB 3.1 standard is backward compatible with USB 3.0 and USB 2.0, Type-A and Type-B adaptors/cables will be required for legacy devices in order to plug into Type-C hosts . Also, adaptors/cables with Type-C receptacles are not allowed. (A hassle, but I can handle that, I think. )

With all of its advantages of performance, charging power and size, it is no wonder that major consumer electronics original equipment manufacturers are pushing semiconductor manufacturers hard to get the silicon that will allow them to turnaround next generation, smaller, faster, and lower power PCs, laptops, tablets, mobile devices and smartphones in time for this year's Christmas season.

Pretty good for a standard that was not only designed by a committee, but by a committee whose members represented the committees at each of the seven companies that started development of USB in 1994 – Compaq, DEC, IBM, Intel, Microsoft, NEC, and Nortel; a standard which is now backed by the 750 companies in the USB Implementer’s Forum (USB-IF).

Embedded.com Site Editor Bernard Cole is also editor of the twice-a-week Embedded.com newsletters as well as a partner in the TechRite Associates editorial services consultancy. If you want to see a calendar of topics for the weekly Tech Focus newsletter or have a topic you would like to see covered, he welcomes your feedback. Send an email to , or call 928-525-9087.

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2 thoughts on “Extending the reach of the USB specification

  1. “It's ironic that in USB 3's quest to remove multiple serial port connectors (MHDL, HDMI, PCI Express, Thunderbolt, etc) it introduces … another connector type! “

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