;Testing Push Button (PB1 and PB2) Switches on Student Project Board. 
;This program gets status of Push Button SW of PB1-PB2 and sends it to LEDs on PORTA 
;Using HCS12 MCU Module with Freescale Student Project Board  
;HCS12 MCU Modules come with USB-BDM and ready to be used with CodeWarrior IDE


;The lower 4 bits of PA3-PA0 (pins of HCS12 CPU) 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 

;The lower 2 bits of PP1-PP0 (pins of HCS12 CPU) are connected to push buttons of PB1 and PB2 permanently
;and must be enabled by clearing bit P5 of PORTP. Also set the PB jumper on UFEA jumpers next to Buzzer



;On HCS12 MCU Module itself 
;a)MAKE SURE BOTH jumpers for PP0 and PP1 are removed (SW1 and SW2).
;b)Also Make sure 8 Jumpers (SW3-1 to SW3-4 and LED1-LED4) on HCS12 MCU module are also removed  
          
;Written and tested by M. Mazidi using 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, %00110000 ;Make PP4 and PP5 as output. On the Project Board, a)the lower 4 pins of PA3-PA0 are connected to LEDs(LED1-LED4) 
        BCLR    PTP,  %00110000 ;and b)the PP0 and PP1 pins are connected to PB1 and PB2 push buttons. c) They mut be enabled by clearing pins P4 and P5 of PORTP
                      ;on Project Board,we need to connect 4 wires from LED5-LED8 (J10) to pins PA4-PA7 via J6 connector (pins 25,27,29,31)
            
                                 
          
;-------Getting Data from PTP and sending it to PORTA

BACK   LDAA PTP
    	 ANDA #$03
    	 STAA PORTA		;Store A into PORTA
	     ;JSR DELAY     ;Optional
	     BRA BACK    
  
;----------DELAY
DELAY

        PSHA		;Save Reg A on Stack
        LDAA    #10		;  
        STAA    R3		;
;--10 msec delay. The HCS12 MCU Module 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