=

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

=


			    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.