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ST43401N/ND and ST43402ND Reference Manual, Rev. C
Section 3. Interface functions
This section provides an overview of the small computer system interface
(SCSI) as it is used in the Elite drive. It is beyond the scope of this manual to
provide a detailed description of all the features, capabilities, variations, and
protocol of SCSI-2. This information is provided in the SCSI Interface
Specification for the Elite Product Family (document 64721702).
All communications between drive and controller must pass through the
interface. This communication includes all commands, status, control signals,
and read/write data transfers. The interface consists of the I/O cables and the
logic (on part of the control board) required to process the signals sent
between the drive and controller.
Dual port drive (ST43402ND) considerations
ST43402ND dual port drives have some different operating limits from the
single port drives discussed in this manual. These differences are listed
below.
• Dual port drives have separate sense buffers, synchronous transfer agree-
ments, and unit attention conditions for each initiator on both ports.
• Any initiator may place commands in the queue on either port.
• Data placed in the cache by one port may be used to satisfy a read request
from the other port. A write from one port may cause data cached by a read
request from the other port to be purged from the cache.
SCSI bus configuration
Figure 11 illustrates the SCSI bus configuration. The SCSI bus can have a
maximum of 16 devices connected to it, and communication can occur
between any 2 devices at any given time. The device that originates an
operation is referred to as the initiator and the device that performs the
operation is the target.
The drive uses one unshielded I/O cable to attach it to the SCSI bus. You must
supply all unshielded cables (see "Guidelines for I/O cabling" in Section 2).
Shielded cables are typically used for connections between cabinets where
electromagnetic compatibility (EMC) and electrostatic discharge (ESD) pro-
tection are required. The I/O cable carries commands, data, and status
information across the SCSI bus. Figure 12 shows the lines (except those not
used) in the I/O cable. The function of each of these lines is explained in
Table 6.
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