Out of band (OOB) signals are used for handshake signaling between a device and its host. In addition the OOB signals ensure that Gen I receivers interoperate with Gen II transmitters. There are three OOB signals:
COMRESET, COMINIT and COMWAKE. Signaling is implemented as a burst of ALIGN primitives, or as a burst of D words composed of four D10.2 characters with a duration of 160 UI.
The COMRESET signaling originates from a host controller and forces a hard reset in the connected device. The COMRESET signal must consist of at least six data bursts.
COMINIT, a request for communication initialization, always originates from the device (hard drive). COMINIT is electrically identical to the COMRESET signal.
COMWAKE may originate from the host controller or the connected device. It is a transmission consisting of six bursts of data separated by an idle bus condition. The signal must contain no less than six data bursts.
Note the eye diagram is not required for compliance but is recommended for fault location and as informational.
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