Int 23H

1 and higher

CONTROL-C/CONTROL-BREAK HANDLER

none

1. –DOS 1.x—

AH = 00h abort program

if all registers preserved, restart DOS call
---DOS 2+---
CF clear
  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

    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

INT 1B,INT 21/AH=92h"PTS-DOS"

Text based on Ralf Brown Interrupt List Release 61