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Pertanyaan
Pembaca SuperUser, Ne Mo ingin tahu apakah keyboard USB hanya mengirim sinyal atau jika mereka menerimanya juga:
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?
Apakah keyboard USB hanya mengirim sinyal atau apakah mereka menerimanya juga?
Jawabannya
Kontributor superuser LawrenceC dan Dmitry Grigoryev punya jawabannya untuk kami. Pertama, LawrenceC:
From the “Device Class Definition for Human Interface Devices (HID)” specification:
Diikuti oleh jawaban dari Dmitry Grigoryev:
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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