User`s manual

Chapter 8: Channel Configuration
8.2.2. Termination
This parameter enables or disables channel SCSI termination on subsystems
featuring SCSI host channels. SCSI buses must be properly terminated at
both ends; that is, when connecting one end of a SCSI cable to a host HBA,
the termination of the channel must be enabled on the subsystem side. An
alternate configuration should be applied when multiple enclosures are
being cascaded on the host buses. An enclosure situated in the middle of a
SCSI bus should have its termination set to disabled.
8.2.3. Default Transfer Clock (in MHz)
These parameters set the data transfer clock rate for synchronous
communication over the SCSI bus, and enable or disable wide transfer,
respectively.
Data transferred across the bus in synchronous transfer mode is clocked
using a synchronous transfer clock signal. The frequency of this signal
determines the rate at which data is transferred. For example, if the
synchronous transfer clock is 10 MHz, data transfer rate will be 10 million
bytes per second (using narrow transfer).
Data transfer across the SCSI bus can be either 8-bits or 16-bits at a time.
The former is referred to as narrow transfer, while the latter is referred to as
wide transfer. According to SCSI channel specifications, transfer speed
shown in MHz is the SCSI bus synchronous frequency. At the same
synchronous transfer clock rate, 16-bit wide transfer rate is double of 8-bit
narrow transfer rate. Please refer to the transfer speed in the table below.
Transfer Rate Clock Speed in MHz
SCSI-320 160MHz
SCSI-160 80MHz
Table 8-3: SCSI Channels Clock Speeds
NOTE:
Infortrend’s SCSI products are backward compatible with older version
of SCSI type. However, using older versions of SCSI type may slow
down the data transferring speed and do not enjoy some of the new SCSI
features.
Under conditions in which SCSI signal quality is poor, such as with
extremely long cables, poor connections, or bad termination, it may
occasionally be necessary to reduce the synchronous transfer clock to allow
the SCSI channel to function normally. Worst case, it may be necessary to
switch to asynchronous communication mode.
User-Configurable Channel Parameters 8-5