;Displaying Overflow Timer on LEDs of PORTA in Assembly for Project Board with HCS12 MCU module using CodeWarrior
;Modified from Example 9-3 in HCS12 book by Mazidi & Causey

;In CodeWarrior,MAKE sure you are in TBDML Mode before downloading 
;Press F7 (to Make), then F5(Debug) to downLOAD,and F5 once more to start the program execution
 

        ABSENTRY Entry        ; for absolute assembly: mark this as application entry point
    
; Include derivative-specific definitions 
		INCLUDE 'mc9s12dp256.inc'     ;
 
 

;code section
        ORG   $4000     ;Flash ROM address
Entry:
	      LDS     #$4000    ;Stack
        LDAA    #$FF
        STAA    DDRA	;Make PA7-PA0 as output
        BSET    DDRP, %00010000 ;the lower 4 bits of PA3-PA0 are connected to LEDs(LED1-LED4) permanently
        BCLR    PTP,  %00010000 ; and must be enabled by clearing bit P4 of PORTP
                                ;We need connect 4 wires from LED5-LED8 to pins PA4-PA7 via J6 connector 
          
;-------
   			
	      LDAA 	#$80			
	      STAA	TSCR1			
	      LDAA 	#$04	    ;Prescaler=16 (Try 0-7 values to see changes on LEDs) 
	      STAA	TSCR2			
	      LDAA	#0			
OVER	  BSET	TFLG2,%10000000	      ;clear the Timer overflow flag (writing HIGH clears it)
H1	    BRCLR	TFLG2,mTFLG2_TOF,H1   ;wait for Timer Overflow
	      INCA				                ;keep adding the overflows
	      STAA	PORTA                 ;and dump it on PORTA to see
	      BRA	OVER                    ;Notice the LEDs of LED1-LED4 on Project Board are arranged in awkward manner.
                              ;LED1 should have been connected to the PA0 pin of CPU ,but instead it is connected to PA3.
                              ;and that is the reason the counter looks awkward.
               

            
;**************************************************************
;*                 Interrupt Vectors                          *
;**************************************************************
            ORG   $FFFE
            DC.W  Entry     ;Reset Vector. CPU wakes here and it is sent to start of the code at $4000