Path: utzoo!attcan!uunet!seismo!sundc!pitstop!sun!decwrl!labrea!rutgers!ucla-cs!jsin
From: jsin@maui.cs.ucla.edu (Jonghoon Sin)
Newsgroups: comp.sys.ibm.pc
Subject: Interfacing to the PC bus
Message-ID: <17932@shemp.CS.UCLA.EDU>
Date: 15 Nov 88 06:23:06 GMT
References: <1717@questar.QUESTAR.MN.ORG> <4617@bsu-cs.UUCP> <90@usl-pc.usl.edu> <616@ablnc.ATT.COM> <764@auvax.UUCP>
Sender: news@CS.UCLA.EDU
Reply-To: jsin@cs.ucla.edu (Jonghoon Sin)
Organization: UCLA Computer Science Department
Lines: 15

I'm posting this for a friend:

  I've built some hardware that interfaces to the PC through three 8 bit
I/O ports.  I've used a 8255 with a couple of other TTL/LS chips as glue.
My questions are:

  1.  In a minimal PC configuration (256K RAM, 1 floppy/controller,
      monochrome card) what port addresses are typically unoccupied?
      Is the area 03C0 to 03CF safe to use?

  2.  I'm finding that the IOW' line is asserted about
      every 15us.  Is this normal?  What's the PC doing?

  I should mention that I'm using a 4.77/8Mhz Taiwanese clone and
  not a True Blue PC.