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    AST RESEARCH, INC.        TECHNICAL BULLETIN # 1122                 4-4-95

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    			    BRAVO MS DRIVE BAY AND ADAPTEC 2940 SCSI

    PROBLEM

    When using an AST drive bay adapter in a Bravo MS 4/66D, with an Adaptec 2940
    PCI SCSI controller, the drive attached to the drive bay adapter is not
    recognized at boot.

    CAUSE

    1. The drive bay adapter is not recognized as the second drive in the system.
    As stated in the Drive bay adapter manual, on page 2,

    "If you have a SCSI drive adapter installed in the desktop computer, make sure
    the memory address for the hard drive adapter is higher than the memory
    address for the SCSI adapter."

    Even though the drive bay adapter is set for a higher address, it is not
    recognized because of the PCI card's unique behavior.  When the system BIOS
    does a ROM scan to initialize each add-in adapter, none of the PCI cards have
    been assigned an address.  After the ROM scan, the system BIOS can determine
    what ROM areas are free, and then program the PCI adapter to reside in one of
    the free areas.  A ROM scan is performed for all of the PCI adapters in the
    system.  Even though the drive bay adapter has the higher address, the Adaptec
    controller will always execute later.  Since the drive bay adapter was
    initialized first, it will be the boot drive, not the SCSI drive.

    2.  The drive bay adapter BIOS is written in such a way that it assumes it is
    the last hard drive adapter in the system.  As such, it does not update
    certain memory locations to identify that a drive exists.  When another hard
    drive adapter such as the Adaptec initializes after the drive bay adapter,
    it can not determine that a drive has already been installed, and will install
    itself.  The drive bay adapter is cut out of the chain for hard disk accesses.

    SYSTEMS AFFECTED
    AST PART NUMBER AND DESCRIPTION

    500985-001     HARD DISK RECEPTACLE PWRE

    501533-XXX     BRAVO MS P60
    501534-XXX     BRAVO MS P90
    501613-XXX     BRAVO MS P90
    501679-XXX     BRAVO MS P60
    501701-XXX     BRAVO MS P75
    501680-XXX     BRAVO MS P90

    SOLUTION

    1.  The PCI system design goal is to make PCI systems self-configuring.
    Any PCI SCSI adapter with a ROM BIOS will behave in the same manner.
    The NCR PCI SCSI adapter used in the Manhattan G systems will work because it
    does not have a ROM BIOS installed on the adapter.

    2.  A new revision of the Hard Drive Bay Adaptec will have BIOS version 1.03,
    which can be installed before an adapter such as the Adaptec 2940.
    Replace P/N 202540-002 revision X03 with revision X04 or higher.  To obtain
    this part, call your local AST Authorized Service Center.