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DTROFF.ASM
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Assembly Source File
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1988-05-27
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2KB
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70 lines
; Program : DTROFF.ASM
; Author : Gary Conway, Infinity Design Concepts, Inc.
; Created : 5/27/88
; Format : COM file
; This program accepts a command line argument that is the COM port number
; The DTR line will be dropped for this com port.
; If no command line argument is given, then no action is taken
; usage: DTROFF 1 -- this would drop DTR on port 1
Main Segment
Assume CS:main,DS:main,DS:main,SS:main
Org 100h
Start: Cld
Mov CX,80 ; max search length
Mov SI,82h ; command line parms start here
FindCmd: Dec CX ; decr counter
Jcxz Exit ; nothing found
Lodsb ; get command line argument
Cmp AL,13 ; end of string ?
Jz Exit ; yeah, get outta here
Cmp AL," " ; skip blanks
Jz FindCmd
Sub AL,"1" ; make it binary
Cbw ; make it a word
Mov [ComPort],AX ; save it
Call GetBase ; calculate base address of comport
Call Comoff ; drop DTR
Exit: Mov AX,4C00h
Int 21h ; exit to DOS
ComOFF Proc
Mov DX,[BaseAddress]
Add DX,4 ; point to modem control register
Mov AL,0 ; clear DTR and DSR
Out DX,AL
Ret
ComOFF Endp
GetBase Proc
Mov DI,[ComPort] ; 0 = COM 1, 1 = COM 2
Add DI,DI
Push ES
Mov AX,40h ; BIOS com segment
Mov ES,AX
Mov DX,ES:[DI]
Pop ES
Mov [BaseAddress],DX
Ret
GetBase Endp
; turn DTR on, on the modem
DTR_ON Proc
Mov DX,[BaseAddress]
Add DX,4 ; point to modem control reg.
Mov AL,1 ; turn on bit 1 (DTR)
Out DX,AL
Ret
DTR_ON Endp
ComPort DW 0
BaseAddress DW 0
Main Ends
End Start