USB Overview

Arduino UNO

<h3 >1. Connecting Things Together</h3><p >For the last decade USB has crept up in popularity because it offers an easy and universal method for very fast data transfer. Printers, cell phones, speakers and a large number of other devices have all adopted the USB standard simple because having this universal connection between devices makes everybody's life easier.</p><figure><img src=https://projects.arduinocontent.cc/a6f4a4ea-8d97-411d-8af1-0bb3796e7622.jpg /><figcaption> </figcaption></figure><h3 >2. Host &amp; Device</h3><p >USB theory is very similar to the way ethernet / internet connectivity theory works. There is one USB Host device and many client devices that communicate with the host device.</p><p >The job of the USB host is to keep track of what type of devices are connected, to which port and what type of data it sends.</p><p >On the other hand the job of the USB device is to tell the Host what type of device it is and then proceed to do whatever it's suppose to do (save data/play music).</p><h3 >3. Specifications</h3><p >There are three different types of USB specifications widely used in the world today. They are all backward compatible with previous revisions, while adding more features and functionality to the existing data bus. The primary difference that the end-user will notice between revisions is data transfer rates are significantly increased, which means less time to save stuff!</p><ul ><li >Connector: 4 Pin (PWR/D+/D-/GND); USB 3.0 - 9pins</li></ul><ul ><li >Power: +5v (no less than 4.75v)</li></ul><ul ><li >Cable Length: 3-5 meter (shorter is better)</li></ul><ul ><li >Cabling: Use Twisted Pair Wiring and Shielding</li></ul><ul ><li >PCB Layout: 90Ω Characteristic impedance, 45Ω Terminations</li></ul><ul ><li >Data: D+/D- differential data lines</li></ul><figure><img src=https://projects.arduinocontent.cc/8576e0ba-cdb3-426f-83ac-336eaea13126.jpg /><figcaption> </figcaption></figure><h3 >4. USB 1.1</h3><ul ><li >Low-speed: 1.5 Mbit/s - (183 kB/s) ~&gt; From USB 1.0</li></ul><ul ><li >Full-speed: 12 Mbit/s - (1.43 MB/s)</li></ul><ul ><li >500mA max current draw per USB channel</li></ul><ul ><li >Only 1 Connector - Type A</li></ul><h3 >5. USB 2.0</h3><ul ><li >High-speed: 480 Mbit/s - (57 MB/s)</li></ul><ul ><li >500mA max current draw per USB channel</li></ul><ul ><li >Connector Types B, C &amp; Mini USB Introduced</li></ul><h3 >6. USB 3.0</h3><ul ><li >Super-speed: 4800 Mbit/s - (572 MB/s)</li></ul><ul ><li >900mA max current draw per USB channel</li></ul><ul ><li >CRC-16/CRC-32 For Header/Payload Protection</li></ul><ul ><li >9 pin Connector Introduced</li></ul><h3 >7. Managing USB devices &amp; Communication</h3><p >The main job of the USB host is to offer and control a pathway for devices to communicate to it. This means a host must keep track of which devices are connected, what type of devices they are, and how much communication bandwidth they need and can receive. Therefore, the USB host controls the device priority and flow of information making a the gate-keeper of the USB communication protocol.</p><p >The USB protocol has a specific set of guidelines for how the USB host should communicate with devices. At a high level, the host is constantly polling devices for their current status. A USB device cannot initiate the communication, that is the job of the USB host. Since the USB Host must control and do so many things at the same time, a USB memory buffers/stack is necessary.</p><figure><img src=https://projects.arduinocontent.cc/6997a5a1-fa38-48da-bec0-d04520357af6.jpg /><figcaption> </figcaption></figure><h3 >8. Types of Communication</h3><p ><strong >Isochronous Transfers:</strong><span > This type of data communication is for real-time, high bandwidth devices like webcams or streaming audio. The USB Host guarantees a specific data-rate will always be available to the USB device that needs this type of communication. Data loss is possible, however unlikely.</span></p><p ><strong >Bulk Transfers:</strong><span > The bulk transfer type of communication is typically reserved for large file transfer like to a USB memory stick or external hard drive storage. This transfer type does not set any guaranteed speed for through-put, so it can be seen as a low-priority communication type for large/long communications.</span></p><p ><strong >Interrupt Transfers:</strong><span > Interrupt driven transfers are meant for devices where low latency and fast response times are necessary. These devices, like a USB mouse or keyboard, do not send much information to the USB Host, but rely on high speed transfers in order to fully-function.</span></p><p ><strong >Control Transfers:</strong><span > The last type of transfer is used in a similar way to the interrupt transfer. Control transfers are typically short commands looking for a status response from a device or host.</span></p>

USB Overview

This lesson is just an introduction to USB in order to give you a working knowledge of what's happening with USB.