Tuesday, February 26, 2019

What is USB (Universal Serial Bus)?

USB is the successor to RS 232, which was implemented in many different ways, causing untold confusion and frustration with the standard. In contrast, the USB is a huge improvement as an industrial standard, which was first developed in about 1990.

The standard defines cables, connectors and communication protocols used in a bus for connection, negation and power supply between computers and electronic devices. USB was initially designed to standardise the connection of computer peripherals including keyboards, pointing devices, digital cameras, printers, portable media players, disk drives and network adapters. It has since become commonplace on other devices, such as smart phones, PDAs and video game consoles, effectively replacing a variety of earlier interfaces including RS 232 and parallel transmission, as well as separate power chargers for portable devices.

As the name says, USB is a serial protocol which means data is transferred bit by bit in an isochronous fashion.


In general, there are three basic formats of USB connectors: the default or standard format intended for desktop or portable equipment (for example, on USB flash drives), the mini intended for mobile equipment (now deprecated except the Mini-B, which is used on many cameras), and the thinner micro size, for low-profile mobile equipment (most modern mobile phones).

There are also five modes of USB data transfer, in order of increasing bandwidth:
·         Low Speed (from 1.0)
·         Full Speed (from 1.0)
·         High Speed (from 2.0)
·         SuperSpeed (from 3.0)
·         SuperSpeed+ (from 3.1)

These modes have differing hardware and cabling requirements. USB devices have some choice of implemented modes, and USB version is not a reliable statement of implemented modes. Modes are identified by their names and icons, and the specifications suggests that plugs and receptacles be colour-coded (SuperSpeed is identified by blue).

Unlike other data buses (e.g., Ethernet, HDMI), USB connections are directed, with both upstream and downstream ports emanating from a single host. This applies to electrical power, with only downstream facing ports providing power. This topology was chosen to easily prevent electrical overloads and damaged equipment. Thus, USB cables have different ends: A and B, with different physical connectors for each.

Therefore, in general, each different format requires four different connectors: a plug and receptacle for each of the A and B ends. USB cables have the plugs, and the corresponding receptacles are on the computers or electronic devices. In common practice, the A end is usually the standard format, and the B side varies over standard, mini, and micro.

(Remember that when referring to receptacles and plugs, they are often called females and males respectively.)

The mini and micro formats also provide for USB On-The-Go with a hermaphroditic AB receptacle, which accepts either an A or a B plug. On-the-Go allows USB between peers without discarding the directed topology by choosing the host at connection time; it also allows one receptacle to perform double duty in space-constrained applications.

There are cables with A plugs on both ends, which may be valid if the cable includes, for example, a USB host-to-host transfer device with 2 ports, but they could also be non-standard and erroneous and should be used carefully.

The micro format is the most durable from the point of view of designed insertion lifetime. The standard and mini connectors have a design lifetime of 1,500 insertion-removal cycles, while the improved Mini-B connectors increased this to 5,000. The micro connectors were designed with frequent charging of portable devices in mind, so they have a design life of 10,000 cycles and also place the flexible contacts, which wear out sooner, on the easily replaced cable, while the more durable rigid contacts are located in the receptacles. Likewise, the springy component of the retention mechanism, parts that provide required gripping force, were also moved into plugs on the cable side.

USB Standard - Development

Now let's have a look at the development of the USB standard. It started in January 1996 with USB One, which defined data transfer rates of 1.5Mbit/s Low Speed and 12 Mbit/s Full Speed. The USB Version 2 was released in April 2000 and ratified by the end of 2001. It introduced a higher data transfer rate, with the resulting specification achieving 480 Mbit/s, an increase of 40 times over the original USB 1.1 specification.

The USB 3.0 specification was published on 12 November 2008. Its main goals were to increase the data transfer rate (up to 5 Gbit/s), decrease power consumption, increase power output, and be backward compatible with USB 2.0. USB 3.0 included a new, higher speed bus called SuperSpeed in parallel with the USB 2.0 bus. For this reason, the new version is also called SuperSpeed. The first USB 3.0 equipped devices were presented in January 2010.

As of 2008, approximately 6 billion USB ports and interfaces were in the global marketplace, and about 2 billion were being sold each year.

Finally, the last version to take note of is the USB C connector Or USB type C.

Developed at roughly the same time as the USB 3.1 specification, but distinct from it, the USB Type-C Specification 1.0 was finalized in August 2014 and defined a new, small reversible-plug connector for USB devices. The Type-C plug connects to both hosts and devices, replacing various Type-A and Type-B connectors and cables with a standard meant to be future-proof, similar to Apple Lightning and Thunderbolt.

The 24-pin double-sided connector provides four power-ground pairs, two differential pairs for the USB 2.0 data bus (though only one pair is implemented in a Type-C cable), four pairs for high-speed data bus, two "sideband use" pins, and two configuration pins for cable orientation detection, dedicated biphase mark code (BMC) configuration data channel, and VCONN +5 V power for active cables. Type-A and Type-B adaptors and cables are required for older devices to plug into Type-C hosts. Adapters and cables with a Type-C receptacle are not allowed.


Having covered the different releases of USB let's have a look at the different connectors used.

Below is a picture of the different connectors. As you can see, up to release three they all have four pins except the mini and micro, which have five pins but the fifth pin is not wired and is used for ID purposes.

The connectors are designed so they cannot be exchanged or plugged in the wrong way to avoid shorts and damage to the equipment. What might be worth mentioning is the Power-use topology. (For more information on topology in networking, visit the website in the recommended reading below.)

The standard connectors were deliberately intended to enforce the directed topology of a USB network: type-A receptacles on host devices that supply power and type-B receptacles on target devices that draw power. This prevents users from accidentally connecting two USB power supplies to each other, which could lead to short circuits and dangerously high currents, circuit failures, or even fire. USB does not support cyclic networks and the standard connectors from incompatible USB devices are incompatible themselves.

However, some of this directed topology is lost with the advent of multi-purpose USB connections (such as USB On-The-Go in smartphones, and USB-powered Wi-Fi routers), which require A-to-A, B-to-B, and sometimes Y/splitter cables. If anybody is interested in the USB on the go connectors please let me know and I will provide more information.


The standard connectors were designed to be robust. Because USB is hot-pluggable, the connectors would be used more frequently, and perhaps with less care, than other connectors. Many previous connector designs were fragile, specifying embedded component pins or other delicate parts that were vulnerable to bending or breaking. The electrical contacts in a USB connector are protected by an adjacent plastic tongue, and the entire connecting assembly is usually protected by an enclosing metal sheath.
The connector construction always ensures that the external sheath on the plug makes contact with its counterpart in the receptacle before any of the four connectors within make electrical contact. The external metallic sheath is typically connected to system ground, thus dissipating damaging static charges. This enclosure design also provides a degree of protection from electromagnetic interference to the USB signal while it travels through the mated connector pair (the only location when the otherwise twisted data pair travels in parallel). In addition, because of the required sizes of the power and common connections, they are made after the system ground but before the data connections. This type of staged make-break timing allows for electrically safe hot-swapping.
Features intended to accomplish extended life, include a locking device, while the leaf-spring was moved from the jack to the plug, so that the most-stressed part is on the cable side of the connection. This change was made so that the connector on the less expensive cable would bear the most wear instead of the more expensive Micro-USB device. However, the idea that these changes did in fact make the connector more durable in real world use has been widely disputed, with many contending that they are in fact, much less durable.

Colour-coded Connectors

Below are images of the different colour-coded USB connectors.

Now let's have a look at the cabling used in USB. USB One and Two used one twisted pair for the data transfer and two wires for the power. Wires are used in different thickness.

Generally wire thickness is expressed in American Wire Gauge the acronym being AWG. The thicker the cable the better the transmission capabilities and the power which can be transmitted. However, to make the cable flexible and thin, the data pair generally uses AWG 26 or 28 and the power 24 or 26. The higher the AWG number, the thinner the cable. Worth mentioning here is also that solid copper wire gives you better transmission capabilities, but since it breaks easily, for short cables stranded wire is chosen. Incidentally superspeed cables will always use 26 AWG.

The maximum length of USB cables is 5 m, if the client needs a longer cable you need a booster.

The Construction of a Good Cable

First off, although most USB cables may look alike externally, the internal wiring may be very different. For this reason, you may find that certain USB cables such as phone chargers are unable to charge your phone, or charge more slowly or faster than the original cable you purchased with your phone. The same principle applies to other uses of USB cables – not all are created equal. 

For the purposes of this article, we’re going to explore the concept of mobile phone USB cables, the majority of which use a USB 2.0 connector. There are five wires inside the USB 1 and USB 2 cables, and there are more inside USB 3.0 cable, which we won’t look at today.

The five wires are:
·2 x 28 AWG data lines
·2 x 20-28 AWG power conductors
·1 x drain wire
These five wires are connected to the five pins in your micro-USB connector.

In fact, there are two kinds of USB cable: fully-rated and sub-channel. The main difference between them is that fully-rated cable can be used for typical peripherals operating at a rate of 480 Mbps (high speed) signalling, while the sub-channel one operates at a rate of 1.5 Mbps (standard speed) signalling. The construction inside the cable fully-rated and sub-channel cable is different.

Like most shielded cables USB cables use an aluminium and a mylar foil, resulting in 100% shielding against interference. Some USB cables use a metal braid, but this is purely for physical protection.

Testing USB Cables

For data, the easiest is to just connect a device to a PC to see whether it works. For charging cables, you can download an app called "Ampere".

However, for more sophisticated and quantity testing, Tektronix and Fluke sell specialised testing equipment.

The test equipment officially supported by the USB forum is the Sigtest tool. You can order this tool and get all the information at www.USB.org.

In Summary

A good cable is defined by the AWG and the shielding used.
For increased strength of the link between the connector and the cable, Teflon can really help the durability of the cable.

To purchase 100% quality tested, custom cables, visit my website at http://www.customcables.co.za 

Recommended Reading


Thursday, August 20, 2015

What is HDMI

What is HDMI

What is H D M I (High Definition Media Interface)?

In simple terms, HDMI is an all digital connection that can carry high-definition video and several digital audio channels all over the same cable. HDMI was first officially unveiled in 2003 but it is only in the last few years that we have seen widespread support for the standard. During the development of HDMI several versions from 1.1 until now 1.4 have been developed. The different versions signify changes to the types of audio they can transmit, all versions should be able to transmit HD video up to 1080p.
1.0 was the first version of HDMI and was ratified in late 2002, it will decode most versions of audio content in DVD and digital TV signals including Dolby Digital and DTS. All HDMI Category 1 Cables are certified up to 720p/1080i.

1.1 this version added DVD – Audio support which means, users with compatible discs and players can listen to 5 channel audio streams without the need for six separate audio RCA cables.

1.2/1.2a: the main improvement of this version over the previous one is the addition of super audio CD support which means users no longer need to rely on I link or analogue cables to listen to super audio. The standard also adds support for an, as yet, unused type of PC connection.

1.3/1.3 a/1.3b/1.3c: these versions added support for Dolby and to high-definition and DTS – HD Master audio, which are used in Blue-ray players. Increasingly, audio and visual receivers are including decoding for these standards on board, while devices like the PlayStation 3 will output the coded signals. The 1.3 standard also increases the available bandwidth by a factor of 2 to 10 Gbps. Although versions 1.3b and 1.3c exist they don't add any further functionality over 1.3 a and so are interchangeable.

1.4 this is the product's biggest update since HDMI was released and introduces a host of new features and a modified cable design. The biggest new feature is the introduction of ethernet to HDMI, which allows a two-way hundred megabit connection to pass between two compatible components and means you will no longer need to wire your system up this land cables as well however, ethernet is an optional feature and not all versions of 1.4 cables supported. You should look for cables marked easy or ”with ethernet.

The 1.4 standard also supports 3-D in full 1080p resolution, where version 1.3 only supports 1080i resolution up to (3840/2160p).
HDMI v1.4 cables support up to 3840×2160 24Hz/25Hz/30Hz, 4096×2160 24Hz.
DSTV / Multichoice currently broadcast their HD Channel on HD 720 (1280 x 720) - 720p.

The new version allows for an audio return channel which is especially handy for television viewers. If you are watching your televisions on-board tuner it means you can now hear it through your sound system with just the single cable - no need for a separate optical cable.

Two new connector systems will also debut with 1.4, a new 19 pin HDMI Micro connector (type D) which is half the size of the current mini, and the automotive connection system (type E), which is designed to withstand the rigours of in car use.

Lastly, HDMI will now support photographic colour standards for better compatibility with digital still cameras.

The two standards are inter-compatible with each other, but to use HDMI ethernet you will need to own dedicated versions of 1.4 cable products, which support the new version. They have been available from early 2010.

But how does HDMI differ to analogue cables?
Analogue video cables, such as component, composite or s – video, are currently still the main methods used to transfer picture signals in an average home system. Component is a highest quality analogue cable, since it breaks down the picture signals into three different cables - one cable each for red, blue and green. When you have got analogue cabling connecting digital sources (such as an LC D or plasma screen with a DVD), the digital video or sound signals have to be converted into analogue to travel through the cable, before being reconverted back into digital at the receiving end. This could lead to some signal degradation and the resulting loss in output quality.

What are the advantages of going digital with HDMI?

HDMI can deliver high-quality sound or vision without the risk of quality loss due to the conversion or compression of the video or audio signal. HDMI pictures should be smoother and sharper with a distinct reduction in video noise. Sound should be crisp and taught, without any distortion. And of course using the single cable HDMI is a lot less messy, than all the additional cables snaking around your home theatre kit.

Because of its digital nature, HDMI also works well with fixed pixel displays such as LCD, plasma or DLP screens and projectors. And HDMI cable allows you to exactly match pixel by pixel in the native resolution with whatever source device you have got connected. HDMI systems will also automatically convert a picture into its most appropriate format, such as 16:9 or 4:3. HDMI has some built in smarts that allow you to control any device connected via HDMI through the one remote. Since the HDMI connection allows two-way communication between devices, it gives you basic universal remote like functions which for example, can tell the components in an HDMI linked system to turn on when you want to watch a DVD, just with the press of a button.

What is the difference between DVI and HDMI?

You may have heard of Digital Video Interface (DVI), which is another all digital connector for video. DVI has been around for longer, and can be found in many more televisions and other devices then HDMI. DVI was initially developed as a connection between PCs and monitors, but eventually found its way into the home entertainment world as well.
The HDMI standard is actually based on the DVI standard, therefore the picture quality should be the same. One advantage of HDMI is the capability of transmitting audio signals, which DVI cannot do, HDMI cables can also be longer than DVI cables, HDMI cables can be up to 20 m in length.
For more information about D V I and conversion from HDMI to DVI see our article on DVI.
(With thanks to CNET Australia).

Thursday, December 19, 2013

What is DVI

What is DVI (Digital Visual Interface)?
According to Wikipedia, DVI is a video display interface developed by the Digital Display Working Group (DDWG). The digital interface is used to connect a video source to a display device, such as a computer monitor. It was developed with the intention of creating an industry standard for the transfer of digital video content.
The interface is designed to transmit uncompressed digital video and can be configured to support multiple modes such as DVI-D (digital only), DVI-A (analog only), or DVI-I (digital and analog). Featuring support for analog connections, the DVI specification is compatible with the VGA interface.[1] This compatibility, along with other advantages, led to its widespread acceptance over competing digital display standards Plug and Display (P&D) and Digital Flat Panel (DFP).[2] Although DVI is predominantly associated with computers, it is sometimes utilized in other consumer electronics such as television setsvideo game consoles and dvd players.
DVI connectors come in several different configurations, which look as follows:

From this it can be seen, that DVI is actually quite confusing, since the same connector (DVI integrated) can be used for both analog and digital output.
So, if one wants to convert from DVI to another format such as HDMI, composite, component or VGA
one needs to establish from the above, which type of DVI your equipment uses and also ensure from the equipment whether the output is digital or analog, if an integrated DVI connector is used.
From that it is easy to see, that conversion from digital DVI to HDMI would be easy and inexpensive,
since both use digital transmission, but a conversion from analog DVI to HDMI would be relative expensive,
since not only would the converter have to change the signals from analog to digital, but also up-scale to the higher resolution of HDMI.

Monday, April 30, 2012

RS232 or "standard" serial cables


Why does my RSS232 cable not work or the myth of the RS 232 not working debunked.

RS 232 serial is an ANSI standard, but there are so many variations of this standard implemented, that it is, for all intents and purposes, not a standard any more…
RS 232 is applicable to both DB9 and DB25 connectors. The connector on a PC is always a male connector; therefore, the connector on the cable must be a female connector. You can see from the tables above, that there are transfer and receive signals, so-called hand shake signals and a chassis- and a reference ground.
Whether the receive and transmit lines are connected cross over or straight depends on what kind of device (peripheral) one wants to link to a PC. The device can either be DTE, or DCE. A PC is normally a DTE device (data terminal equipment) a modem would be a DCE device (data communication device). The problem is that you normally don’t know what kind of device your peripheral is.
Another problem is the length of the cable, the standard allows for a maximum length of 15 m, but we have successfully implemented cables with 200 m and more, the links depends completely on your computer and your peripheral.
Perhaps we should here give a short explanation of what a serial standard is. The most common standards are RS232, USB, FireWire and SATA.
In these standards data is transmitted in a serial method, that means that all characters which are sent one after the other on one wire and all received characters are on a different wire, in comparison to a parallel method where all the bits are transmitted on a different wire.
Although all the above are serial standards the way of transmitting is completely different, therefore, a ‘translation’ has to be made from one standard to the other.
From the above, it might become apparent that a conversion from USB to RS232 can be difficult if one does not know what kind of device the RS232 peripheral is.
But if one knows, what type of device is to be connected, a cable can be built to change from the standard DTE to DCE and the required handshake.

Saturday, March 22, 2008

Computer and Electronic Cables and Connectors, protocol convertors, KVM switches

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We specialise in making up cables to your requirementsand can help you with technical advise,
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We have a large stock and invite you to have a look at some items we are presently overstocked in
and want to dispose off at really low prices.
The side is: http://www.volkirk.co.za to have a look and also visit our e-shop at http://www.customcables.co.za.