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124 Parallel SCSI Interface Product Manual, Rev. A
than 509 would transfer 509 bytes of data plus 3 bytes of pad plus 4 bytes of iuCRC for a total transfer of
516 bytes). The target shall not set the data length to a value that exceeds the maximum burst size as
defined in the disconnect-reconnect page (see Seagate SCSI Command Reference Manual, Part number
100293068.)
[5] The BIDI Direction field determines the data direction if the command is a bidirectional command and the
type code is data or data stream. The code values for the BIDI Direction field are defined below.
Table 51: BIDI Direction
[6] The iuCRC Interval field contains the length in bytes of the data to be sent before a iuCRC is transferred.
The iuCRC interval length shall not include the 4 byte iuCRC nor any transmitted pad bytes (e.g., an
iuCRC interval length of 510 transfer 510 bytes of data plus 2 bytes of pad plus 4 bytes of iuCRC for a
total transfer of 516 bytes). The iuCRC interval shall be a multiple of two (i.e., odd numbers are not
allowed). If the iuCRC interval is equal to zero or is greater than or equal to the data length only one
iuCRC shall occur at the end of the SPI information unit.
[7] The iuCRC field shall use the algorithm defined in Subsection 11.3 of the ANSI SCSI Parallel Interface
(SPI-5).
Codes Description
00b
A unidirectional command or a type code other than data or data stream (see Table 50).
01b
A bidirectional command transferring data from the SCSI initiator device to the SCSI target
device.
10b
A bidirectional command transferring data from the SCSI target device to the SCSI initiator
device.
11b
Reserved.