ESI Command Sequence
A SCSI Send Diagnostic command or Receive Diagnostic Results command is sent from the host computer to the disk-drive to initiate an SES transfer. The Disk-drive then asserts "-PARALLEL ESI" to begin this sequence of ESI bus phases:
| Phase | Function | |
| Discovery phase | Disk-drive tests that the enclosure is SFF-8067 compliant | |
| Command phase | Disk-drive sends the SCSI CDB to the enclosure (similar to the write phase) | |
| Either | Read phase | Disk-drive sends diagnostic page data to the enclosure |
| or | Write phase | Disk-drive receives diagnostic page data from the enclosure |
Finally, the disk-drive deasserts "-PARALLEL ESI".
The above sequence is just a simple implementation of a 4-bit wide parallel interface which is used to execute a SCSI transaction. If the CDB is for a Send Diagnostic command then the data is sent to a SCSI diagnostic page in the enclosure. If the CDB is for a SCSI Receive Diagnostic Results command then the data is received from a SCSI diagnostic page. No other CDB types are allowed.
Read more about this topic: Enclosure Services Interface
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