Usability and "upside down" connectors

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Usability and "upside down" connectors

Post  meodingu on Mon Jan 10, 2011 5:51 pm

Usability and "upside down" connectors
It is by design difficult to attach a USB connector incorrectly. Most connectors cannot be plugged in upside down and it is clear from kinesthetic sensation of making a connection when the plug and socket are correctly mated.
However, it is not obvious whether the connector should be face up or face down, and thus it is often necessary to try the insertion both ways. The side of the connector on a USB cable or other product with the "USB Icon" (trident logo) should be "visible" to the user during the mating process. Some manufacturers do not, however, make the trident logo on USB cables easily visible or detectable by touch.[citation needed] Additionally, Some computers such as the Mac Mini, have the ports vertically, in many Japanese computers and other devices, the trident logo on the cable or other USB device being inserted must be facing down, while in many American computers and devices the logo must be facing up.[citation needed] However, this is not always the case, such as with some Dell (an American company) computers.[citation needed]
Officially, the USB 2.0 specification states that the required USB Icon is to be "embossed" ("engraved" on the accompanying diagram) on the "topside" of the USB plug, which "provides easy user recognition and facilitates alignment during the mating process."[15] The specification also shows that the "recommended" (optional) "Manufacturer's logo" ("engraved" on the diagram but not specified in the text) is on the opposite side of the USB Icon. The specification further states "The USB Icon is also located adjacent to each receptacle. Receptacles should be oriented to allow the Icon on the plug to be visible during the mating process." However, the specification does not consider the height of the device compared to the eye level height of the user, so the side of the cable that is "visible" when mated to a computer on a desk can depend on whether the user is standing or kneeling. Although published eight years later, the USB 3.0 specification has similar wording, stating only "USB 3.0 receptacles should be orientated to allow the Icon on the plug to be visible during the mating process."[16]
Only moderate insertion/removal force is needed (by specification). USB cables and small USB devices are held in place by the gripping force from the receptacle (without need of the screws, clips, or thumbturns other connectors have required). The force needed to make or break a connection is modest, allowing connections to be made in awkward circumstances (i.e., behind a floor-mounted chassis, or from below) or by those with motor disabilities. This has the disadvantage of easily and unintentionally breaking connections that one has intended to be permanent in case of cable accident (e.g., tripping, or inadvertent tugging).
The standard connectors were deliberately intended to enforce the directed topology of a USB network: type A connectors on host devices that supply power and type B connectors on target devices that receive power. This prevents users from accidentally connecting two USB power supplies to each other, which could lead to dangerously high currents, circuit failures, or even fire. USB does not support cyclical networks and the standard connectors from incompatible USB devices are themselves incompatible. Unlike other communications systems (e.g. RJ-45 cabling) gender changers make little sense with USB and are almost never used, though cables with 2 standard type A plugs are commonly found in North American dollar stores.

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