ColdFire/68K Microcontrollers and ProcessorsのトピックRe: USB receptable type

USB receptable type

cédricmarmonier — Thu, 19 Apr 2018 12:31:17 GMT

Hello,

When you connect 2 OTG systems with a micro-USB cable, host must be micro-USB type AB and device must be micro-USB type B, isn't it ?
I don't understand why phone connectors are micro-USB type B and not micro-USB type AB : someone know why ?

A phone can be connected to a PC : it would be normal that phone connector is micro-USB type B because VBUS is powered by PC.
... But a phone can be connected to a phone : it is why, it would be more logic that phone connector is micro-USB type AB.
Problem is when I check a phone, I see micro-USB connector is type B and not type AB. With micro-USB type B connector, you can't use micro-USB type A cable and with micro-USB type AB connector, you can use all micro-USB cable type : why phone manufacturers doesn't use micro-USB type AB connector to be compatible with all cable type ? I think there is a reason, isn't it ?

I must develop a USB OTG product (not a phone) and I would to know if I must use micro-USB type AB or type B.

Re: USB receptable type

TomE — Fri, 20 Apr 2018 07:40:49 GMT

> When you connect 2 OTG systems with a micro-USB cable, host must be micro-USB type AB

> and device must be micro-USB type B, isn't it ?

Not according to Wikipedia:

https://en.wikipedia.org/wiki/USB_On-The-Go#OTG_micro_plugs

Micro-A adapters allow for connection to standard-A plugs, as used on fixed or standard devices. An OTG product must have a single micro-AB receptacle and no other USB receptacles.

I don't understand why phone connectors are micro-USB type B and not micro-USB type AB : someone know why ?

Maybe because they don't support, and don't want to support OTG. If you want a keyboard or external audio, use Bluetooth.

With OTG the "magic happens" because of the cable:

An OTG cable has a micro-A plug on one end, and a micro-B plug on the other end.

Tom

Re: USB receptable type

cédricmarmonier — Fri, 20 Apr 2018 15:05:56 GMT

Not according to Wikipedia:..

Wikepedia isn't a trusted source of information but I checked Wikipedia information in USB standard. It write in USB official documentation :

An OTG device is required to have one, and only one USB connector: a Micro-AB receptacle as defined in [Micro-USB1.01].

The Micro-AB receptacle is only allowed on OTG products. All other uses of the Micro-AB receptacle are
prohibited. The Micro-AB receptacle accepts either a Micro-A plug or a Micro-B plug.

=> OTG product must use Micro-AB receptable and no-OTG product must use Micro-B receptable. A product with micro-USB receptable which can supply VBUS must be mandatorily OTG (It must be micro-AB).

Maybe because they don't support, and don't want to support OTG. If you want a keyboard or external audio, use Bluetooth.

Recent phones can supplies VBUS (ie : you can use USB key => they are OTG). USB standard is defined by a group composed of main manufacturers (USB.org - About USB-IF), it is shocking that phones which are manufactured by them aren't in confirmity with USB standard : perhaps, there is an amendment for battery powered devices which permitted micro-B receptacle for OTG products (but I don't find this information in USB standard).