;Getting data from 8 DIP SW of PORTB and sending it 8 LEDs on PORTA 
;with HCS12 MCU Module from Axiom using Freescale Student Project board  
;HCS12 MCU Modules come with USB-BDM. This code is for CodeWarrior IDE

;In HCS12 MCU Module RAM address is from $1000-3FFF 
;We use RAM addresses starting at $1000 for scratch pad (variables) and $3FFF for Stack

;The lower 4 bits of PA3-PA0 are connected to LEDs(LED1-LED4 on J10) permanently
;and must be enabled by clearing bit P4 of PORTP. Also set the LED jumper on UFEA jumpers next to Buzzer
;We also need to connect 4 wires from LED5-LED8 (J10) to pins PA7-PA4 via J6 connector 

;See Toggling PORTA sample code for Student project Board on this website.


;On Project Board,
;a)We need to connect 8 wires from SW1-1,2,3,3 and SW2-1,2,3,4 (on J10) to pins PORTB7-PORTB0 (via J6 connector)
;b)Notice on J6 of project Board PORTB7-PORTB0 are pins 41,43,45,47,49,51,53,55


;On HCS12 MCU Module itself,
;a)MAKE SURE ALL the jumpers for PORTB are removed.(SW3-1...SW3-4 and LED1-LED4) 
;b)The 8 Jumpers (SW3-1...SW3-4 and LED1-LED4) on HCS12 MCU module connect the PORTB to SW and LEDs of the Module itself.  
;c)The PORTB can be either used by the HCS12 MCU Module itself or the Project Board, but not both of them at the same time.            

;Written and tested by M. Mazidi from examples in Chap.4 of HCS12 textbook 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 'mc9s12dt256.inc'     ;CPU used by Axiom board
 
 
;----------------------USE $1000-$2FFF for Scratch Pad 
R1      EQU     $1001
R2      EQU     $1002
R3      EQU     $1003

;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    #$0
        STAA    DDRB	;Make PB7-PB0 as input 
                      ;We need connect 8 wires from SW1-1,2,3,3 and SW2-1,2,3,4 (on J10) to pins PB7-PB0 via J6 connector 
          
;-------Get data from DIP SW of PORTB and send it LEDs on PA7-PA0 of PORTA

BACK   LDAA PORTB   ;Get data from PORTB 
    	 STAA PORTA		;and send it to PORTA
	     
	BRA BACK    
  
;----------DELAY
DELAY

        PSHA		;Save Reg A on Stack
        LDAA    #10		;Change this value to see  
        STAA    R3		;how fast LEDs Toggle
;--10 msec delay. The Axiom board works with XTAL=4MHz 
;Freq. for Instruction Clock Cycle is 2MHz (1/2 of 4MHz). 
;(1/2MHz) x 10 Clk x10x200=10 msec. Overheads are excluded in this calculation.         
L3      LDAA    #10
        STAA    R2
L2      LDAA    #200
        STAA    R1
L1      NOP         ;1 Intruction Clk Cycle
        NOP         ;1
        NOP         ;1
        DEC     R1  ;4
        BNE     L1  ;3
        DEC     R2  ;Total Instr.Clk=10
        BNE     L2
        DEC     R3
        BNE     L3
;--------------        
        PULA			;Restore Reg A
        RTS
;-------------------

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