9

EDIT: After looking at the connector with a endoscope's camera it turns out I've missed some pins. They are far less visible than other 8. The D+/D- and CC are there. This makes the example unsuitable. It still leaves the question of what spec allows open. DT70/64GB

I've just bought a USB flash drive, a Kingston DataTraveler 70 (DT70/64GB).

Its Type C interface has only 8 pins:

A1  A2  A3  A4  A5  A6  A7  A8  A9 A10 A11 A12
NC  NC  NC  NC  NC  NC  NC  NC  PR PR  PR  PR

NC  NC  NC  NC  NC  NC  NC  NC  PR PR  PR  PR
B12 B11 B10 B9  B8  B7  B6  B5  B4 B3  B2  B1


NC = not connected
PR = present

The pins that are present are only GND, V+, and two SuperSpeed differential pairs.

There is no D+/D1 USB 2.x differential pair, and no CC1/CC2.

I've tried reading the spec for USB 3.2, but I couldn't find any passage that would clearly state USB 2.x lines are mandatory or optional for a device.

It's obviously terrible design for a USB flash drive not to support 2.x host, but is this legal from a specifications perspective?

lynx
  • 109

2 Answers2

11

Googling would have resolved this pretty quickly. Yes, this should work, without backward compatibility: 1, 2

Yes, the D+ and D- lines are only needed on 1.x, 2.0 and 3.0 devices; in 3.1+ devices they can be omitted (at least, not routed to the controller) and it should be possible to establish a USB connection.

However, this is the technical perspective; from the certification standpoint such a device would still be "illegal" (noncompliant) and should not be called a "USB device" at all.

One caveat would be: you wouldn't be able to boot from this USB mass storage, as firmware (which performs the initial load of the OS from the flash) often uses a USB 2.0 connection even on 3.x-capable hardware.

psmears
  • 549
Nikita Kipriyanov
  • 3,249
5

In response to:

Do you know what part of the spec mandates compatibility?

USB 3.2 revision 1.1, section 11.3 "USB 3.2 Device Support for USB 2.0" states:

USB 3.2 device certification requirements require support for USB 2.0 for all user attached devices.[...]
The USB 2.0 capabilities of a USB 3.2 device shall be designed to the USB 2.0 specification and shall meet the USB 2.0 compliance requirements

It's safe to say that it should be impossible for a device with no D+ and D- pins to meet USB 2.0 spec and therefore the USB 3.2 spec.

Note the exception:

For product installations where support for USB 3.2 operation can be independently assured between the device and the host, such as internal devices that are not user accessible, device support for USB 2.0 may not be necessary.

Themoonisacheese
  • 688