Šodienas jautājumu un atbilžu sesija mums priecājas par SuperUser - Stack Exchange dalību, kas ir kopienas vadīta Q & A tīmekļa vietņu grupa.
Jautājums
SuperUser lasītājs Ne Mo vēlas zināt, vai USB tastatūras nosūta signālus vai arī tos saņem arī:
A USB keyboard does not need to receive any signals from a computer, just power, right? Or does it need to receive signals as well as send them?
Vai USB tastatūras tikai sūta signālus vai arī viņi tos saņem arī?
Atbilde
SuperUser autori LawrenceC un Dmitrijs Grigorjevs mums ir atbilde. Pirmkārt, LawrenceC:
From the “Device Class Definition for Human Interface Devices (HID)” specification:
Seko Dmitrija Grigorjeva atbilde:
Any USB device regardless of its class requires bidirectional communication to function. Every USB device (or function in terms of USB specifications) is represented as a set of endpoints which can be thought of as buffers which accept or receive data. However, even endpoints which can only send data wait for a special packet called a token before they can reply:
Even so-called interrupt transfers are done in this way, with the USB host polling connected devices using token packets. What differs between regular (bulk) transfers and interrupt transfers is that the polling time is small and guaranteed in the latter case. Still, all transfers are initiated by the host.
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Attēla kredīts: Lūka Jonesa (Flickr)