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Wikipedia states:

An OTG product must have a single Micro-AB receptacle and no other USB receptacles. An OTG cable has a micro-A plug on one end, and a Micro-B plug on the other end

Micro-A is apparently similar to the standard Micro-B plug, but without chamfered corners:

micro usb plugs

A Micro-AB receptacle is also rectangular.

However, in practice, all of my phones that support USB OTG have Micro-B receptacles, not Micro-AB. And the OTG cable I have it front of me has a Micro-B plug. Also if you google photos of "OTG Cable" they all show Micro-B plugs

In fact I can't remember ever seeing a Micro-A plug. Is this something that Wikipedia has totally made up? Or is it something that is in the USB spec but the entire electronics industry wisely chose to ignore?

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  • \$\begingroup\$ The Sony Mini Pro phone has the rectangular USB Mico-AB receptable. You can use both micro-A and micro-B USB OTG adapters with it. \$\endgroup\$ – Turbo J Apr 1 '15 at 10:17
  • \$\begingroup\$ I have seen them. But in the end, is there any usb devices that conforms to even 50% of the spec? It all starts with the current they draw... \$\endgroup\$ – PlasmaHH Apr 1 '15 at 10:32
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    \$\begingroup\$ "A Micro-AB receptacle is also rectangular." There is no such thing as a Micro-A receptacle. The one in your picture is the Micro-AB receptacle. MicroUSB Specification defines Micro-B plug and receptacle, Micro-AB receptacle, and Micro-A plug. \$\endgroup\$ – endolith Oct 19 '16 at 14:38
  • \$\begingroup\$ Oh wait, those are pictures of plugs, not receptacles. \$\endgroup\$ – endolith Oct 19 '16 at 14:45
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    \$\begingroup\$ @jpsmith As endolith said there is no such thing as a micro-A receptacle. If it has a rectangular receptacle that is micro-AB so you should be able to use an ordinary micro-B cable in it. \$\endgroup\$ – Timmmm Mar 21 '17 at 14:23
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Yes. Pretty much ignored in favor of the micro-B. There is no "Micro-A receptacle" since the micro-AB covers both. There were many more orders for micro-B cables than there were receptacles, and the industry quickly scrapped the micro-A.

The last of its kind.

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    \$\begingroup\$ You should add a bit of context to the image? \$\endgroup\$ – user2943160 Jun 24 '16 at 0:34
  • \$\begingroup\$ Looks like a USB OTG cable with a Micro-A plug. \$\endgroup\$ – Timmmm Jun 24 '16 at 7:12
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The definitive answer is in the USB OTG specification, the current revision is 1.0

On a quick read, Section 3.13 states

The OTG supplement defines the following additional connectors: Mini-A plug and receptacle, and Mini-AB receptacle.

and

Any device with a Mini-AB receptacle shall meet all of the requirements and provide all the functionality of a dual-role device.

You can check the details, but that implies that presence of the AB does require all the functionality, but there are connectors defined which could be used on an OTG device which doesn't meet all the functionality.

If you find Wikipedia is incorrect after you've read the document, please share the knowledge and update it with specific references as well as confirming here.

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    \$\begingroup\$ He's talking about micro, not mini. The rules are not the same for both. For example, USB has deprecated mini-A and mini-AB connectors. \$\endgroup\$ – dim Jun 24 '16 at 8:35
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It is rather uncommon.

You would find it in a device that is so small that a standard A connector wouldn't fit, but where the device would still be host only. I can't think of any good examples quickly, which should give you an idea why they are uncommon.

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