; user control of carrier detection. BYERSX Auxiliary
;
bdos	equ	5
fcb	equ	05ch
;
	aseg
	org	0100h
;
	lxi	h,0
	dad	sp
	lxi	sp,stack
	push	h
	mvi	c,87
	lxi	d,0
	call	bdos
	ora	a
	lxi	d,norsx
	jz	exit
	mvi	c,84;		system state
	mvi	e,0ffh;		enquiry
	call	bdos
	sta	state
	lxi	h,fcb
	mov	a,m
	ora	a
	jnz	help
	inx	h
	mov	a,m
	cpi	'O'
	inx	h
	mov	a,m
	jnz	help
	inx	h
	cpi	'F'
	jz	off
	cpi	'N'
	jz	on
;	"	"
; give help
help:	lxi	d,hlpmsg
;	"	"
; message and exit
exit:	mvi	c,9
	call	bdos
	pop	h
	sphl
	ret
;
; suppress carrier checks
off:	mov	a,m
	cpi	'F'
	jnz	help
	inx	h
	mov	a,m
	cpi	' '
	jnz	help
	lda	state
	ani	NOT 010h;	disable checks
	mov	e,a
	mvi	c,84
	call	bdos
	lxi	d,offmsg
	jmp	exit
;
; enable DCD checks
on:	mov	a,m
	cpi	' '
	jnz	help
	lda	state
	ori	010h
	mov	e,a
	mvi	c,84
	call	bdos
	lxi	d,onmsg
	jmp	exit
;
hlpmsg:	db 'usage: DCDCHECK [ON|OFF] (controls DCD monitoring)$'
offmsg:	db 'Not '
onmsg:	db 'Checking for carrier$'
norsx:	db 'BYERSX not running$'
;
state:	ds	1;		BYERSX input state
;
	ds	48
stack:	ds	0
;
	end