USB Connectors
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                                        Rev. 18-Apr-2023


Five different basic types of USB connector:  A, B,  Mini
A and B,  Micro A and B, and C.  The micro connector comes
standard on most non-Apple mobile phones and on many other
portables, though USB-C connectors are slowly replacing
them in the newest generation of devices.


The standard micro connector has  five  pins in its 2.0
version and  ten  pins in the less common 3.0 generation:


The fourth pin (mode detect) is also commonly referred to as
USB “On-the-Go” or simply “OTG.”  This pin allows devices to
switch between host and peripheral roles.  In a smartphone,
for instance, the USB connection might allow the phone to
perform as a mass storage device when connected to a
computer, but as a host to read data from removable storage.

This OTG pin is also what allows devices to “decide” which
will draw power from the other – typically the host will
supply power to the peripheral, though in some cases the
roles may be re-negotiated.


Looking at the micro connector on a cable, all generations
have pins numbered 1-5,  from left to right on the main
trapezoid  (looking into the cable connector with the pins
on the bottom.  Third generation connectors have pins 6-10,
ascending, from left to right, on the added side rectangle.


Looking into a Micro Cable Connector:

     1          2          3          4          5
  -------    -------    -------    -------    -------
    Vcc       Data -     Data +     ID Pin     Ground
   +5 V                            for OTG
   VBus


Looking into an old normal USB "A" Cable Connector:


     4          3          2           1
  -------    -------    -------     -------
   Ground     Data +     Data -       Vcc
                                     +5 V
                                     VBus


The USB "C" type connector is the one with 2 rows of
12 pins each  and  it can plug in either right side up
or up side down.  USB "C" connector supports both USB 2.0
with its one pair of Data lines and USB 3.0 with its
two additional pairs of Data lines.



The 2 original USB connectors, both 4 pin, were the USB A
connector  (large standard rectangular)  and  the UBS B
connector  (large square with 2 rounded corners and used
mostly on things like printers and scanners).


There were two types of "mini" connectors:  mini A
and mini B.  These were about the same width as the
newer "micro" connectors but about twice the thickness.
I think that both  mini A  and  mini B  have both mostly
gone away.


I still do not full understand why there are both
Micro A plugs  and  Micro B plugs ?   There is a common
Micro AB Receptacle  and  a specific Micro B Only Receptacle.
The Micro A plug is basically rectangular.  The Micro B plug
is a trapezoid.  The contact pins and the latch appear to
be basically the same on Micro A and Micro B plugs.

Micro A plugs are typically used to plug into a “master”
device, such as a computer.  Micro B plugs connect to a
“slave” device, such as a printer or cell phone.

A Micro-B receptacle will only work with a micro-B plug.

A Micro-AB receptacle will work with both micro-A and
micro-B plugs.


The standard micro connector is available only up to the
second-generation USB standard, though a less common and
much wider 3.0 version exists.  The 3.0 version offers:

  - Better transfer rates than 2.0, but it's less practical
    than the smaller and faster USB-C connector.

  - Receptacles that can accept older generation cables,
    but older receptacles cannot accept 3.0 cables.