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Technotools
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Technotools (Chestnut CD-ROM)(1993).ISO
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lang_c
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mikecom
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dtr.asm
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Assembly Source File
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1987-05-15
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1KB
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39 lines
title DTR SET/RESET
include subfx.h
; Mike Dumdei, 6 Holly Lane, Texarkana TX 75503
;******************************************************************************
; ASYNC_DTR -- Sets or clears 'data terminal ready' based on passed flag.
; Returns R_NOPORT if port invalid else returns R_OK.
;******************************************************************************
begseg COMM_TEXT
publicproc _async_dtr
push bp
mov bp,sp
push si ;stack frame setup
call __ck_port_arg ;ck if valid, load pointers
jz dtr_exit ;bad arg if ZR flag set
mov dx,COM_BASE
add dx,4 ;xFC)modem control register
in al,dx
cmp Flag,OFF
jne dtr_on
and al,n B_DTR ;clear DTR bit
jmp s snd_MCRbyte
dtr_on:
or al,B_DTR ;set DTR bit
snd_MCRbyte:
out dx,al ;send new mask to UART
xor ax,ax ;returning R_OK
dtr_exit:
pop si
pop bp
ret ;restore regs and exit
_async_dtr endp
endseg COMM_TEXT
end