# Compound device

> Mediated Wiki article. Canonical URL: https://mediated.wiki/source/Compound_device
> Markdown URL: https://mediated.wiki/source/Compound_device.md
> Source: https://en.wikipedia.org/wiki/Compound_device
> Source revision: 1070955254
> License: Creative Commons Attribution-ShareAlike 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/)

A USB '''compound device''' contains an embedded [USB hub](/source/USB_hub) and one or more non-removable USB devices.<ref>{{Cite web|last=|first=|date=|title=USB 2.0 Specification|url=https://www.usb.org/document-library/usb-20-specification|url-status=live|archive-url=https://web.archive.org/web/20190413224102/https://www.usb.org/document-library/usb-20-specification |archive-date=2019-04-13 |access-date=2020-11-30|website=USB-IF}}</ref>  It may or may not have exposed downstream ports.

The internal USB hub may be a physical [IC](/source/Integrated_circuit) that connects to other ICs, or the hub and all functions may be implemented in software on a single IC (though it is more common to integrate them as a ''[composite device](/source/composite_device)'' in this case).  Compound devices have separate device addresses assigned to the hub and each downstream function, while composite devices have a single address.  The hub's [descriptors](/source/USB_descriptor) indicate whether it is part of a compound device or a regular hub with only removable devices.

This arrangement is used by wireless receivers for [cordless keyboard](/source/Alphanumeric_keyboard)s and [mice](/source/Mouse_(computing)) (where the mouse and keyboard are separate devices connected to the compound device) and sometimes for [printer](/source/computer_printer)s which have [memory card](/source/memory_card) slots.

== References ==
{{Reflist}}

{{DEFAULTSORT:Compound device}}
Category:USB

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Adapted from the Wikipedia article [Compound device](https://en.wikipedia.org/wiki/Compound_device) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Compound_device?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.