If Information Units is enabled (parallel SCSI only), the drive will drop the bus on detecting a CRC error during a LQ_IU. If the CRC error occurs during the Information Units command phase or data out phase, the drive will return CHECK CONDITION with a CRC error. Additional sense is set to 4703h (Information Unit CRC error detected).
On detecting an Initiator Detected error, the drive will return CHECK CONDITION with additional sense of 4800h (initator detected error message received). The exception is when Information Units mode is enabled (parallel SCSI only), when one of the following occurs:
•If an IDE message is received during a LQ_IU, the drive drops the bus and retries the LQ_IU pair.
•If the message is received during Status IU, the drive retries the LQ_Status pair.
•If the message is received during Data IU, the drive sends a LQ_Status with CHECK CONDITION and additional sense of 4800h.
Disconnect strategy
The disconnect strategy used by the drive is based on maximizing the use of the bus for large sequential data transfers from a large data buffer. The drive will disconnect whenever it believes that it will provide better bus use. This may be between command and data phases, between bursts of data or before sending status. However, the drive will guarantee that it sends the configured maximum burst size or the remaining data in the transfer in any single data phase burst if the maximum burst size has been set to a value other than zero.
The following diagram gives an overview of the drive’s disconnect strategy:
16 Interface Implementation