Configuration Byte Description And Defaults; Scsi Subsystem Data Structure - Adaptec AHA-1740A Technical Reference Manual

EISA-to-Fast SCSI Host Adapter
Refer to Appendix D, EISA Free-Form Data for the initial SCSI subsystem data
structure.

Configuration Byte Description and Defaults

The following describes the SCSI device configuration byte format. Firmware default
values are also given. These defaults are used by the firmware to interface with the
various targets in the event that no Initialize SCSI Subsystem command has been re-
ceived by the host adapter.
Byte 0
Bit 7 - Allow removable media in BIOS disk scan
This bit is used by the host adapter BIOS only, it does not affect operation. When this
bit is set, the BIOS will include a removable media device in the scan for devices to
support under Int 13h.
This feature does not support removal or exchange of the media. The drive is
treated as a fixed media drive only. This is primarily intended to allow boot from a
removable media disk drive.
Bit 6 - More than one LUN supported
This bit is used by the host adapter BIOS only. When set, this bit indicates that the
target will support more than one LUN. In the default state, only LUN 0 is supported
for each SCSI target.
Bit 5 - Parity Check enable
When set, parity will be generated and checked. When cleared, parity will be gener-
ated but not checked. By default, parity checking is enabled for all targets.
Bit 4 - Send Start command
This bit is used by the host adapter BIOS only. When set, the BIOS will send a Start
Stop Unit SCSI command to the target after a Test Unit Ready command returns a
check condition and reports a not ready status. The Start Stop Unit command will set
the Immed and Start bits and will clear the LoEj bit as defined in the SCSI 2 specifi-
cation. By default, this feature is disabled for all targets.
Bit 3 - Synchronous Negotiation enable
When set, the host adapter will initiate synchronous negotiation with this target.
When cleared, the host adapter will not initiate negotiation, but will respond if the
target initiates negotiation. Default is to initiate synchronous negotiation with all
targets.
Bit 2 - Disconnection enable
When set, the host adapter will allow disconnection to occur with this target by set-
ting the Allow Disconnection bit in the ID Message. When cleared, the Allow
Disconnection bit will be cleared. By default, disconnection is enabled for all targets.
Hardware Functional Description
Note
4-29