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orientation is maintained throughout the bus.
Pin 1 of the SCSI cable is designated by a colored
stripe on one edge of the flat ribbon cable. Pin 1 of
the host adapter or SCSI device connector is
usually designated by a delta or arrow symbol ( )
on the connector.
The internal connectors for SCSI Channel A and
SCSI Channel B (AHA-2740-T/2742-T only) use a
50-pin SCSI flat ribbon cable with a 50-pin header
internal connector.
External SCSI Cables
The external connector for SCSI Channel A uses a
50-pin shielded cable with a high-density external
connector. External cable connectors are keyed and
can only be plugged in one way; Pin 1 orientation is
automatic.
Floppy Cables (AHA-2742/2742-T only)
The floppy connector uses a 34-pin floppy ribbon
cable with a 34-pin header connector. Make sure to
maintain Pin 1 orientation as previously described
in Internal SCSI Cables.
Termination on the SCSI Bus
The first and last physical SCSI devices on the
ends of the SCSI bus must have a set of resistors
called terminators either installed or enabled. All
other SCSI devices installed between the ends of
the SCSI bus must have their terminators either
removed or disabled.
Terminating the Host Adapter
The factory installed bus terminators on the host
adapter are enabled by default. Host adapter
termination should be disabled if you attach SCSI
devices to both internal and external connectors,
since the host adapter would then be in the middle
of the SCSI bus. Table 3 describes the three
possible SCSI device and host adapter (AHA)
configurations.
Table 3. SCSI Device and AHA Configuration
Devices Connected To Host Adapter
Internal devices only (AHA at end of cable)
External devices only (AHA at end of cable)
Internal and External devices (AHA in between)
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Enabling or disabling host adapter termination is
software selectable only. To disable termination on
the host adapter, refer to Section
the Host Adapter for instructions.
Terminating Other SCSI Peripheral Devices
Check the manufacturer's documentation to
determine how to enable or disable SCSI bus
termination on your SCSI peripheral device(s).
SCSI ID Setting
For each device located on the SCSI bus, a unique
SCSI ID (0-7) must be reserved. The default value
for your host adapter is SCSI ID 7. Refer to Section
, Configuring the Host Adapter for instructions on
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changing the SCSI ID for the host adapter. Refer to
the SCSI device documentation for information on
changing the SCSI ID on other SCSI devices.
Reassemble the System
Follow your system and SCSI device documenta-
tion to replace the system cover and connect all
system and SCSI device power cables.
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Configuring the Host Adapter
A Configuration diskette containing an EISA
Configuration utility is normally supplied by the
EISA system vendor. Depending on the EISA
Configuration utility supplied with your system,
host adapter configuration will vary. The basic
steps involved in running the EISA Configuration
utility are explained in this section.
Run the EISA Configuration Utility
Place the bootable Configuration diskette in an
operative drive and reset the system to boot from
this diskette. Run the EISA Configuration utility
as instructed by the EISA system vendor.
Copying Files
The Configuration utility typically allows you to se-
AHA Termination
lect among a number of options, including copying
On/Enabled
new configuration files. Select this option to install
On/Enabled
the !adp7771.cfg and adp7770.ovl files from the
Off/Disabled
host adapter diskette to the bootable Configuration
diskette. If the Configuration utility does not
, Configuring
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provide such an option, you can also use the DOS
Copy command to copy these files to the bootable
Configuration diskette.
Select the Host Adapter
Once the files have been copied, run the option in
the Configuration utility that allows you to
configure the EISA slot in which the host adapter
is installed. A screen listing the host adapter
parameters is displayed.
Note
If your host adapter is an AHA-2740-T/2742-T, a set of
parameters for SCSI Channel B is displayed and can be
configured.
Configure the Host Adapter Parameters
Select values for each setting as instructed on the
screen's menu.
Interrupt Level–selects the IRQ level of the host
adapter.
Bus Release Time–selects the EISA bus release
time used when the host adapter gets preempted in
bus master mode.
Data FIFO Threshold–selects the data FIFO
threshold percentage used by the host adapter.
Host Adapter BIOS Address–selects the base
BIOS address of the host adapter.
Host Adapter SCSI ID–selects the SCSI ID (0-7)
for the host adapter. SCSI IDs 0 and 1 should be
reserved for SCSI hard disk drives. Each installed
SCSI device must have a unique SCSI ID.
SCSI Bus Parity–allows you to enable or disable
SCSI bus parity on the host adapter.
SCSI Selection Timeout–selects the SCSI
selection timeout used by the host adapter during
the SCSI selection phase.
SCSI Bus Reset at Power-on–allows you to
enable or disable a SCSI bus reset generated by the
host adapter during its power-on initialization, and
after a Hard Reset.
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