最終更新:2015-03-09 (月) 18:44:57 (3328d)  

USB/ロースピード
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1.5Mbps

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Low-speed Keep-alive

  • All hub ports to which low-speed devices are connected must generate a low-speed keep-alive strobe, generated at the beginning of the frame, which consists of a valid low-speed EOP (described in Section 7.1.13.2). The strobe must be generated at least once in each frame in which an SOF is received.
  • This strobe is used to prevent low-speed devices from suspending if there is no other low-speed traffic on the bus. The hub can generate the keep-alive on any valid full-speed token packet. The following rules for generation of a low-speed keep-alive must be adhered to:
    • A keep-alive must minimally be derived from each SOF. It is recommended that a keep-alive be generated on any valid full-speed token.
    • The keep-alive must start by the eighth bit after the PID of the full-speed token.



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