- The USB device not only helps in establishing a flawless communication but also assists to power up the connected peripheral devices, setting you free from the parallel ports and the external power chargers that turn out to be costly and cover more space.
Introduction to USBThe USB is an industry standard mainly developed for laying out the communication between a computer and peripheral devices.
- Additionally, unlike some traditional connector, USB doesn't require any user adjustable interface setting, it serves more like a plug and play device. You just need to connect the one end of the USB cable with a peripheral device and another end to the computer and start playing and controlling the peripheral device.
- The USB is unable to handle multi-master arrangement and can support one host per bus. However, the "USB on the GO" is designed with the purpose, if there is no host available, two devices collaborate with each other to define, which one is appropriate to serve as a host in the whole protocol.
USB PinoutFollowing figure shows the pinout of the Universal Serial Bus. A number of USB connectors are available. The connector attached with the host (computer) or device is called male port or receptacle, and the connector coupled with the cable is called female jack or plug.There are 7 USB connectors introduced until now
- Standard-A Type
- Standard-B Type
- It comes very handy in a variety of fast charging applications, as it features power delivery, video, audio, and data capability in a single package.
Pin DescriptionAs mentioned above USB is a serial bus that is housed with 4 shielded wires where two are reserved for power (+5v & GND) while the other two are used for carrying differential data signals. They are marked as D+ and D- on the pinout given above and are transmitted on a twisted pair.
- The NRZI (Non-Return to Zero Invert) encoding scheme is mainly employed to send data with a sync field while ultimately helps in synchronizing the host and receiver clocks.
CapabilityA single USB bus can handle around 127 devices at a time. If you plan to connect more devices, you need to add another host to the arrangement.
- The earlier USB hosts came with two ports that were enough to control the peripherals devices at that time. However, with the invention of new devices and as all workload was shifted to computer technology, it ultimately put the burden and erupted the need for more ports incorporated into the USB hosts.
- The USB 1.1 comes with a maximum cable length of 5 meters that can easily support peripheral devices running at speed around 12 Mbit/s, however, it varies as the cable length differs i.e. cable length of around 3 meters is a good fit for devices running at a low speed of around 1.5 Mbit/s.
- The USB 3.0 is not reserved for specific cable length, however, the cables used under this standard must meet some electrical specifications i.e. the maximum practical length is 3 meters for copper cabling with AWG 26 wires.
USB VersionsA number of USB versions have been released until now with every new version disguising the features of its predecessors with some added speed and connection capability.Following table shows the list of USB versions introduced till date.
ArchitectureThe USB architecture is mainly based on tiered star topology that is identical to 10BASE-T Ethernet. The topology interface supports the need of hub as per requirements.Recently, some devices like Keyboard come with a USB hub and instead of directly connecting the mouse or any digital camera with a computer, you can connect them with the hub incorporated on the keyboard and use them similar as you connect them with the computer, as eventually the keyboard will be connected to the computer at the other end. The tiered star topology comes with a number of advantages that put it ahead of using a daisy-chaining connection for the peripheral devices.
- It is incorporated with built-in protection interface that disconnects the connected device immediately in case it comes under the radar of sheer current - more than it can handle. You can use other devices as usual with the disconnection as it won't be affecting other devices in the whole arrangement.
How does it WorkAs the peripheral device is connected to a USB host, the enumeration process is activated which is nothing but the process of detecting, identifying and loading drivers for a USB device.
- It all gets triggered by sending a reset signal to the USB device. Once the connected device is reset, it is assigned a unique 7-bit address by the host.
AdvantagesThe USB comes with a number of advantages that make it an ideal choice for communication purpose. Yes, parallel and serial ports come handy in some PLC programming and computational purpose, but where communication is required with a decent pace that involves no human interference, USB grooves its way brilliantly.Following are some major advantages of USB over other means of communication.
- It is a user-friendly and common person with no technical skills can easily get benefit from the sheer advantages of USB protocol. And the flexible interface of USB sets you free from the hassle of using a plethora of connector and wires at the back of your PC, that may turn your working space into a lot of mess.
As you connect the USB peripheral device with the USB hub on the computer, it starts configuration automatically and strives to keep the device quite in line with the working environment of the host, giving you the prompt signal your connected device is ready to use for the required operation.
----- For example, when you connect your phone with the computer, it gets configured automatically. And some phones which don't get connected will give you the option, indicating you need to install the specific driver in order to control the cell phone from your computer.
- Recent computers come with USB hubs that can easily support 4,5 ports as per your needs. In case your requirements surpass the given ports, you can add external USB hubs to incorporate more ports into the computer.
Low cost and power consumption are remarkable features that make USB stay ahead of its counterparts. It mainly works on 5V with little power consumption around 500 mA for USB 2.0 and 2.5 mA for USB 3.0.
- As mentioned earlier, the USB comes with a built-in current protection interface that saves the host from going over current that can ultimately put the host in a total stall. The current protection feature blocks the current that gets beyond the recommended ratings.
LimitationsThere are some limitations involving the use of USB in terms of bigger perspective. The USB cables are limited in length, making them vulnerable for their use in distant areas.
- You can benefit USB protocol on the same surface, covering less distance where whole arrangement for communication between the peripheral devices and computer is laid out in a single tabletop surface.
- For example, the USB to parallel port converter supports connection with a printer, but it doesn't work properly with the scanner due to the absence of bi-directional data pins.