;-------------------------hex16in routine begins--------------------------+
; from BLUEBOOK OF ASSEMBLY ROUTINES FOR IBM PC & XT.
;         page : 51
;
; NAME HEX16IN
; ROUTINE FOR Conversion from ASCII Hexidecimal to 16-bit binary
;
; FUNCTION: This routine accepts a hexidecimal number from the std input
; device and converts it to internal 16-bit binary form.
;
; INPUT: The individual digits of the hexxidecimal number are received in
; ASCII through a call to a std I/O routine.  The valid digits are 0 - 9
; and A - F.  An ASCII code for other than a valid digit will terminate
; the routine.
; OUTPUT: A 16-bit binary number is returned in DX.
; REGISTERS USED:  Only DX is modified.  It returns the result.
; SEGMENTS REFERENCED:  None
; ROUTINES CALLED:  STDIN
; SPECIAL NOTES: None
;
; ROUTINE TO CONVERT FROM ASCII HEXIDECIMAL TO INTERNAL 16-BIT BINARY.
;
hex16in	proc	far
;
	push	cx		; save registers
	push	ax
;
	mov	dx,0		; initialize DX
;
hex16in1:
	call	stdin		; a digit comes in in AL
	sub	al,30h		; reduce from ASCII
	jl	hex16in3	; check if too low
	cmp	al,9
	jle	hex16in2	; go of OK
	and	al,5Fh		; for lower case too
	sub	al,7		; adjust for A - F
	jl	hex16in3	; too low for A - F
	cmp	al,15		; check if too high
	jg	hex16in3
;
hex16in2:
	cbw			; convert to word
	mov	cl,4		; for a count of four
	sal	dx,cl		; shift DX left
	add	dx,ax		; add in digit
	jmp	hex16in1
;
hex16in3:
	pop	ax		; restore registers
	pop	cx
	ret			; return
;
hex16in	endp
;-------------------------hex16in routine ends---------------------------+