; #########################################################################################
; # Indiana University                                                                    #
; # Computer Science Department                                                           #
; #                                                                                       #
; # Example Program #1 (C335 Lab Tutorial)                                                #
; #                                                                                       #
; # DESCRIPTION:                                                                          #
; #                                                                                       #
; # 68K assembly language program to output the characters of the string "HELLO" on the   #
; # PC terminal (hyperterminal) using TRAP #15 mode 1. As each character in "HELLO" is    #
; # output, a counter is incremented and displayed on the target's seven segment display  #
; # using TRAP #15 mode 4. TRAP #15 mode 0 is used to terminate the program's execution.  #
; #                                                                                       #
; # AUTHOR:                                                                               #
; # Bryce Himebaugh (bhimebau@cs.indiana.edu)                                             #
; # IUCS Staff                                                                            #
; # 6/17/99                                                                               #
; #                                                                                       #
; #########################################################################################


	SECTION code
START:                            ; "START" label required (debugger) at beginning of code 
        clr.b d2                  ; initialize loop counter to be put on 7 segment display
        lea message,a0            ; load the base address of "message" into A0
loop:
        move.b (a0)+,d0           ; put a char from "message" in D0 and point at next char
        beq exit                  ; exit if a 0 (end of message) was just moved to D0 
        moveq.l #1,d1             ; setup to cause a TRAP #15 putchar to terminal 
        trap #15                  ; execute putchar
        nop                       ; NOP to deal with debugger TRAP anomoly 
        addq.b #1,d2              ; increment the current count value.   
        move.b d2,d0              ; load the current loop count value into D0
        moveq.l #4,d1             ; setup to cause a TRAP #15 write to 7-segment display 
        trap #15                  ; execute write to 7-segment display  
        nop                       ; NOP to deal with debugger TRAP anomoly
        bra loop                  ; branch back to get the next character in "message". 
exit:
        clr.b d1                  ; setup to cause the TRAP #15 to terminate the program 
        trap #15                  ; execute program termination 
message:
        dc.b "hello",0