From: Craig.Orr@f263.n633.z3.fidonet.org (Craig Orr)
Newsgroups: comp.sys.ibm.pc.hardware
Subject: Programming OPTI motherboard chipset?
Date: Thu, 31 Dec 1992 09:17:00

 > From: antony@werple.apana.org.au (Antony Suter)
 > Organization: werple public-access unix, Melbourne

 > I have a 386/40 motherboard with an OPTI chipset. My
 > AMI bios is the
 > latest type yet seems to be an early version of this
 > type (ie. the
 > Advanced BIOS). My BIOS doesnt give me the option of
 > running my ISA
 > bus at anything other than 8MHz.

 > Can someone tell my how to program the chipset to
 > change the bus speed?

 > (from memory its the 381/382 chipset,
 > the cache is Write Back.)

Firstly... 8MHz is the recommended BUS Speed, Use above this frequency
could/will cause instability and potential/probable data loss!

I Don't have the programming manual for the 381/382, but I
do have the 281/2 manual. They may be similar...

Quoting Relevent Sections...

An Indexing scheme is used to access all the registers. Port 22H is used as an
indexing register and port 24H is used as the data register. Every access to
port 24H must be preceeded by a write to port 22H even if the same register
data is being access again. All reserved bits are set to zero by default.

blah blah blah

Now... This is where incompatibility might occur 8^) 'cause from memory the
381/2 support more  ATCLK speeds than the 281/2, but still...

Index 14H - Misc. Control Register

  Bit            Function                       Default

   0             ATCLK (Bus Speed) Select         0
                 0 = CPUCLK / 6
                 1 = CPUCLK / 4
   1             Enable Turbo Switch              0
                 0 = Disabled
                 1 = Enabled
   2             Slow Refresh Mode                0
                 0 = 15.9 microsecs
                 1 = 95.5 microsecs
                 (I tried this once, the system really
                 speeds up, but floppies slow down to
                 a crawl)
   3             Reserved                         0
   4             Fast NMI Request                 0
   5             Master Byte Swap Enable          0
   6             Keyboard Reset Control           0
                 1=Execute HLT before Chipset will
                 generate a CPU RESET from keyboard
                 controller  (ie: Gate A20)
   7             Znith Mode Enable                0
                 1=allow F0000H-F0FFFH to be
                 written whislt write protect is
                 turned on


Sorry that the info isn't exactly as required, I have reqested later chipset
documents and will see what comes in.

Until then this might help, my guess is that they use the reserved bit, or have
reorganised the structure a little.

Can anyone else make comments to enlighten?

One Other Hint... As almost ALL motherboards based on Opti Chipset are the
DemoBoard Layout each and every other manufacters BIOS should work on your
machine, It's just a matter of finding one with the options you want enabled!
Find a supplier who sells
Opti Motherboards and try to BUY/BORROW one of their BIOS's. It should work!

Another Hint... Find a person who has a copy of AMIBCP (AMI BIOS Control
Program) and get them to rewrite your BIOS after enabeling the missing
settings. I have noticed that all AMI BIOS's have ALL the settings, but each
and every manufacturer of Motherboards who uses AMI BIOS chips is able to turn
on or off each and every feature in the BIOS!!!


Craig Orr
Of Course All standard disclaimers apply to this information!

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Newsgroups: comp.sys.ibm.pc.hardware