IBM XT diagnostic ROM - test-drb@ccmp.vtda.org

28 May 2008

IBM XT diagnostic ROM

Jim Leonard trixter at oldskool.org
<mailto:cctalk%40classiccmp.org?Subject=IBM%20XT%20diagnostic%20ROM&In-Reply
-To=20080528131358.V82915%40shell.lmi.net> 
Wed May 28 15:49:36 CDT 2008 

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Fred Cisin wrote:
...
  What you have found is called a Power On Self Test
card, or "POST card".

 During the cold start process, the computer sends numbers at various
 stages to a port.  By putting in a card that decodes the port and displays
 those numbers, you can see which stages of the start up process succeeded.

 It will only work if the computer is making it at least partway through
 the cold start boot process, and will certainly not tell you anything if
 the CPU is dead, no matter what some brain-dead moron might say.  (Well,
 OK, some also have a few LEDs to tell you if the power supply is live,
 etc.) 
It was my understanding that only AT-class machines (by age, not 
necessarily by architecture type) wrote to that port.  I've never seen a 
PC or XT (or clone thereof) motherboard/BIOS write to that port.
-- 
Jim Leonard (trixter at oldskool.org
<http://www.classiccmp.org/mailman/listinfo/cctalk> )
http://www.oldskool.org/
Help our electronic games project:           http://www.mobygames.com/
Or check out some trippy MindCandy at     http://www.mindcandydvd.com/
A child borne of the home computer wars: http://trixter.wordpress.com/

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------REPLY------

Hi,
The IBM XT does send POST codes to port $60 during start up.  The AT and
later send more detailed codes to port $80 which almost all POST card
devices support.

http://bioscentral.com/postcodes/ibmbios.htm

You can make your own POST card type device.  I have two already but one is
a dedicated AT style and the other is an AWARD SOFTWARE POSTcard Rev 1.3.
Unfortunately, I do not have the manuals necessary to change the onboard
configuration switches to convert it from AT only to support XT style POST
codes.

http://members.tripod.com/~BBright/information/postcard.htm

Thanks to all who replied and for any help in repairing this classic IBM XT
motherboard.

Andrew Lynch

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