1 ; Program to read, store and echo string of 20 ASCII characters and sum up any integers
 2 ; Modified for Easy68K simulator - uses Easy68k trap instructions for I/O
 3 ;  Sum in D2 at end, display on screen
 4 
 5 start:	org		$1000
 6 		move.w	#2,d0		; set up registers for trap instruction to read string
 7 		move.w	nchar,d1	; number of characters to read in d1 (80 max)
 8 		lea		msg,a1		; load the address of msg in a1 (must use LEA)
 9 		trap	#15			; do EASY68k I/O operation
10 		move.w	#0,d0		; display string on screen
11 		trap	#15			; do EASY68k I/O operation
12 		
13 ; begin processing
14 
15 		clr 	d2 			; clear the register for the sum
16 		jmp 	enter 		; enter loop at end
17 loop:	move.b 	(a1)+,d0 	; move the character from msg array to d0
18 		jsr 	addit 		; subroutine to test and add integers
19 enter: 	dbra 	d1,loop 	; subtract 1 from d1 and see if done
20 
21 ; all data processed, sum in d2 - now display number on screen
22 
23 		move.l 	d2,d1		; put result in d1 for EASY68k I/O
24 		move.w	#3,d0		; display number on screen
25 		trap	#15			; do EASY68k I/O operation
26 
27 		STOP	#$2000 		; end of program
28 
29 ; Subroutine addit tests ASCII characters to see if they represent numbers
30 ; and if so, adds them to the sum in d2
31 
32 addit: 	and.b 	#$7F,d0 	; mask off parity bit of character
33 		cmp.b 	#$30,d0 	; see if it is less than $30
34 		blt 	skip 		; if so, skip to return statement
35 		cmp.b 	#$39,d0 	; see if it is greater than $39
36 		bgt 	skip 		; if so, skip to return statement
37 		and.w 	#$000F,d0 	; get the number
38 		add.w 	d0,d2 		; add to sum in d2
39 skip: 	rts 				; return from subroutine
40 
41 		org		$2000		; data storage area
42 msg: 	ds.b 	80			; storage for string of ASCII characters
43 nchar: 	dc.w 	20 			; number of characters to read
44 		END		START