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Magnum One (Mid-American Digital) (Disc Manufacturing).iso
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swplpt_a.arc
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SWAPLPTS.ASM
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Assembly Source File
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1991-04-12
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1KB
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48 lines
page 60,132
title SWAPLPTS - Swap LPT1 and LPT2
;
; S W A P L P T S . A S M
;
; Copyright(C) 1991 John W Grothman. All rights reserved.
;
; Released to the public domain.
;
; purpose:
; Swap LPT1 and LPT2.
;
; to do:
;
; technical notes:
; This is a SIMPLE thing to do. Just swap the base I/O addresses
; in low DOS memory that DOS uses to map the LPT port hardware.
;
; modification log:
; 1.0 4/12/90 John W Grothman (CompuServe 73740,1540)
cseg segment para public 'code'
assume cs:cseg, ds:cseg, es:cseg, ss:cseg
org 100h
begin proc near
xor ax, ax
mov ds, ax ; set DS to 0 (DOS low memory (data) area)
mov bx, 0408h ; low DOS memory offset of LPT1 base I/O address
mov ax, [bx] ; get it and
mov dx, ax ; save in DX
mov bx, 040ah ; low DOS memory offset of LPT2 base I/O address
mov ax, [bx] ; get it and
mov cx, ax ; save in CX
mov ax, dx ; get back LPT1
mov [bx], ax ; and put it in LPT2
mov bx, 0408h ; address of LPT1 base I/O address
mov ax, cx ; get back LPT2
mov [bx], ax ; and put it in LPT1
mov ax, 4c00h ; terminate with ERRORLEVEL = 0
int 21h
ret
begin endp
cseg ends
end begin