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From: dcr0801%ritcv@cs.rit.edu
Newsgroups: comp.unix.i386
Subject: How to enable 24-bit addresses (Answer to Access over 1MB)
Message-ID: <1447@cs.rit.edu>
Date: 16 Dec 89 18:04:35 GMT
Sender: news@cs.rit.edu
Reply-To: dcr0801%ucss@cs.rit.edu ()
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Organization: Rochester Institute of Technology, Rochester, NY
Lines: 19

I'd like to thank everyone who responsed to my question about accessing
memory over 1 Meg. in protected mode on an IBM.  Here is the answer:

   System Control Port A (0x92) can be used to enable or disable the 
   Alternate Gate Address 20 signal.  When Bit 1 of this port is set to
   0, address lines 20-23 are forced to 0.  This way, any address 
   generated over 20 bits (access over 1MB) will be wrapped around to
   the lower Meg.  Enabling this signal (setting Bit 1 on) will allow
   the full address (24 bits in 80286) to be placed into the address
   bus. (IBM Tech. Ref. , Compatability Section, page 3-26,3-23,3-38,3-50
   for the PS/2 Models 50,60,70, and 80 respectivily.)


Thanks again for everyone that replied.  I hope this information will help
someone else out of a bind in the future.

Dave Rein (dcr0801@ultb.isc.rit.edu)   "I just goes to show what you can do
										if you're a total psychotic"
											  - Woody Allen