Odd problem with int 0x21, ah = 0x4A

From	Freedom on the Oceans <alex.buell@munted.org.uk>
Newsgroups	comp.os.msdos.programmer
Subject	Odd problem with int 0x21, ah = 0x4A
Date	2011-04-28 15:18 +0100
Organization	One very high maintenance cat
Message-ID	<ci9o88-tf01.ln1@nntp.local.net> (permalink)

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I have the following applet:

	BITS 16
	ORG 0x100
 
	mov	ax, ss
	mov	dx, es
	sub	ax, dx
	mov	bx, sp
	shr	bx, 4
	add	bx, ax
	mov	ah, 0x4A
	int	0x21
	ret

In the debugger, all segment registers all point to the same segment of
memory which is OK. After the call, DS gets trashed but everything looks
OK. I checked with the Ralf Brown's interrupt lists but it doesn't
mention anything about DS getting trashed. Any ideas why? 
-- 
Tactical Nuclear Kittens

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Odd problem with int 0x21, ah = 0x4A Freedom on the Oceans <alex.buell@munted.org.uk> - 2011-04-28 15:18 +0100
  Re: Odd problem with int 0x21, ah = 0x4A Jim Leonard <mobygamer@gmail.com> - 2011-04-28 10:58 -0700
    Re: Odd problem with int 0x21, ah = 0x4A Freedom on the Oceans <alex.buell@munted.org.uk> - 2011-04-28 19:30 +0100
  Re: Odd problem with int 0x21, ah = 0x4A "R.Wieser" <address@not.available> - 2011-04-28 22:57 +0200
    Re: Odd problem with int 0x21, ah = 0x4A Ross Ridge <rridge@csclub.uwaterloo.ca> - 2011-04-30 01:02 -0400
      Re: Odd problem with int 0x21, ah = 0x4A Freedom on the Oceans <alex.buell@munted.org.uk> - 2011-05-01 08:48 +0100
        Re: Odd problem with int 0x21, ah = 0x4A "R.Wieser" <address@not.available> - 2011-05-01 13:43 +0200

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