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23

Category: DOS kernel

INT 23 - DOS 1+ - CONTROL-C/CONTROL-BREAK HANDLER

---DOS 1.x---
Return: AH = 00h abort program
	if all registers preserved, restart DOS call
---DOS 2+---
	CF clear
Return: all registers preserved
	return via RETF with CF set or (MS-DOS 1,DR DOS) RETF 2 with CF set
	    DOS will abort program with errorlevel 0
	else (RETF/RETF 2 with CF clear or IRET with CF ignored)
	    interrupted DOS call is restarted
Notes:	this interrupt is invoked whenever DOS detects a ^C or ^Break; it
	  should never be called directly
	MS-DOS 1.25 also invokes INT 23 on a divide overflow (INT 00)
	MS-DOS remembers the stack pointer before calling INT 23, and if it is
	  not the same on return, pops and discards the top word; this is what
	  permits a return with RETF as well as IRET or RETF 2
	MS-DOS 2.1+ ignores the returned CF if SP is the same on return as it
	  was when DOS called INT 23, so RETF 2 will not terminate the program
	Novell DOS 7 always pops a word if CF is set on return, so one should
	  not return with RETF 2 and CF set or IRET with the stored flags' CF
	  set
	any DOS call may safely be made within the INT 23 handler, although
	  the handler must check for a recursive invocation if it does
	  call DOS
SeeAlso: INT 1B,INT 21/AH=92h"PTS-DOS"

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  Copyright 2000   by Ralf Brown     Updated Jul 2000