;Testing Push Button (PB5-PB8) Switches on Student Project Board. 
;This program gets status of Push Button SW of PB5-PB8 and sends it to LEDs on PORTA 
;Using HCS12 MPU Module with Freescale Student Project Board  
;HCS12 MCU Modules come with USB-BDM and ready to be used with CodeWarrior IDE

;In HCS12 MCU modules 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 Student Project Board, We need to 
;a)connect 4 wires from push button PB5-PB8(on J10) to pins PORTB3-PORTB0 of J6 connector (pins 47,49,51,53 of J6) 
;b)Notice on J6 of Project Board PORTB3-PORTB0 are pins 47,49,51,53,55

;On HCS12 MCU Module itself 
;a)MAKE SURE ALL jumpers for PORTB are removed (LED1-4 and SW3-1 to SW3-4).
;b)The 8 Jumpers (SW3-1 to 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 PORTB3-PORTB0 as input 
                      ;We need connect 4 wires from PB5-PB8 of J10 to pins PORTB3-PORTB0 via J6 connector 
          
;-------Get data from Push Botton SW of and send it LEDs on PORTA

BACK   LDAA PORTB   ;Get data from PORTB (Push Button PB5-PB8 on Project Board are active Low).    
    	 STAA PORTA		;and send it to PORTA (Press any Push Button (PB5-PB8) and LEDs of PORT will go LOW
	     
	      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