Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!cs.utexas.edu!csd4.milw.wisc.edu!uxc!uxc.cso.uiuc.edu!ux1.cso.uiuc.edu!uxa.cso.uiuc.edu!mms00786
From: mms00786@uxa.cso.uiuc.edu
Newsgroups: comp.sys.ibm.pc
Subject: Re: Protected mode and PC/XT cards
Message-ID: <111700101@uxa.cso.uiuc.edu>
Date: 10 Jun 89 22:42:00 GMT
References: <158322@neabbs.UUCP>
Lines: 21
Nf-ID: #R:neabbs.UUCP:158322:uxa.cso.uiuc.edu:111700101:000:879
Nf-From: uxa.cso.uiuc.edu!mms00786    Jun 10 17:42:00 1989


Hello Hardware Experts:

I am a summer intern designing an I/O card for the AT. In other words, I am
supposed to respond to the -IOW and -IOR signals. In looking through the 
IBM AT Hardware Tech. manual, I noticed that in their Prototype board, they
decode only A0 through A9 (for a total of 1K io channels). But I am under the
impression that the '286 (and the 8086, 8088 etc) all have a possible 64K of 
IO space. 

So, why don't they decode all 16 lines A0 through A15? Their IO space map
also covered only the bottom 1K of IO space, so I am working under the 
assumption that there is some sort of gentleman's agreement not to use space
above that, or their bus controller generates IOW and IOR only for the bottom
1K. Hope I am assuming right. I start building the board Monday, so any 
response will be greatly appreciated.

Thank You,
Milan.
mms00786@uxa.cso.uiuc.edu
.