1
\$\begingroup\$

I'm trying to get a concrete answer on what determines DRD support... the port type (USB-C) or the protocol type (USB 3.1). Besides the poor naming scheme with USB 3.0/3.1/3.2, there's a lot of lacking communication about the DRD device support (being able to act as a device or host).

According to https://blogs.synopsys.com/tousbornottousb/2018/05/03/usb-dual-role-replaces-usb-on-the-go it is any USB spec at or above 3.1, but it also confusingly talks about being Type-C

This Intel page talks about having DRD with USB 3.2 Gen 1x1 (5 Gb/s) with no mention of Type-C.

Wikipedia mentions DRD on their USB Type-C page, but not on their USB 3.1 page.

I'm trying to find some kind of authoritative answer on this question, if possible

\$\endgroup\$
2
  • \$\begingroup\$ Wikipedia states "USB Dual-Role-Device capabilities introduced with the USB 3.1 specification". \$\endgroup\$
    – Finbarr
    Mar 20, 2021 at 0:03
  • \$\begingroup\$ Right, but I believe USB 3.1 might be possible with a Type-A and Type-C connectors, but I'm suspecting Type-A may be incompatible with OTG / DRD. Ale's response below also suggests the same. \$\endgroup\$
    – Wisteso
    Mar 20, 2021 at 3:36

1 Answer 1

1
\$\begingroup\$

Dual-role USB ports were introduced in so-called "On-The-Go" (OTG) supplement to USB specifications. (still cannot figure out what OTG means). The role swap came at the expense of introducing one extra pin - ID pin. Therefore originally only mini- and micro-USB ports can provide the swap function, and Type-A can't provide the swap. Additional function of source-sink swap was provided at DC level, called "accessory charging".

Type-C Cable and Connector Specification is the next step in providing flexibility to USB. Type-C specifies new CONNECTOR, which can carry various data protocols, although originally it was supposed to be only USB. Thus the Type-C is the standart nearly independent from USB (or anything else), and USB2, 3.x or 4 don't matter.

Keep in mind that there are two basic roles of a port - power role, and data role. Since USB is a host-centric protocol, this distinction is quite important. So four combination of roles are possible. Type-C basic (DC-based) communication functionality (over CC pulls up-down) defines only the default swap function - either a host (and a power source), or a device (and a power sink). To provide two other configurations (host-sink and device-source), a negotiation over additional protocol is required. It is implemented within Power Delivery protocol over the same CC wire using serial communication messages.

\$\endgroup\$
4
  • \$\begingroup\$ This is nicely explained. Just to confirm... this means Type-A can never be OTG / Dual Role? However Type-B, Mini, Micro, and Type-C are able? The power / data part makes sense, and that part was fairly clear, but I didn't know about the extra pin needed to facilitate swapping. \$\endgroup\$
    – Wisteso
    Mar 20, 2021 at 3:34
  • \$\begingroup\$ @Wisteso, No, Type-B port is only for devices, and thus is not "swappable".. Mini and micro ports must be of dual "A/B" type to be "swappable", although the industry abandoned "A/B" and used only B-type receptacles in formal violation of OTG specs. \$\endgroup\$ Mar 20, 2021 at 15:36
  • \$\begingroup\$ Okay that makes sense. So basically Type-C is the only type that can flip between both then? (Due to non-conformance to OTG) Otherwise you have to be device-only (B, micro, mini) or host-only (A)? \$\endgroup\$
    – Wisteso
    Mar 20, 2021 at 23:02
  • \$\begingroup\$ " (still cannot figure out what OTG means) " It was called "on the go" because it was built for use on portable devices. A device large enough for 2 USB ports would not need a dual role port since there is a port for both roles. It is a violation of the spec to have both OTG and more than 1 USB port. Large devices needing both roles, such as a printer that is a client to a computer and host to a flash drive, will not be expected to require disconnection from the computer to read files from the drive. Acting a USB client to 2 hosts is somewhat nonsensical as that is best by a network. \$\endgroup\$
    – MacGuffin
    Jun 16, 2021 at 11:36

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.