lab02.asm

; Name:         David Chapman
; Program:      Lab 02
; Version:      1.0
; Date Started: 10/15/2014
; Last Update:  NA
;               Copyright © 2014
;
; Description:  Implement a counter that increments the count when SWX is
;               pressed and clears the count when SWY is pressed. The count
;               is to be displayed via the four LEDs that were used in the
;               last Lab. You get to choose the two switches that increment
;               and clear (these should be chosen from the switches used in
;               the previous lab). Be sure to use the debouncing method
;               covered so that you do not add to your count when you do not
;               need to.

;******************************************************************************
;-----------------------------Include Libraries--------------------------------
            INCLUDE    'derivative.inc'              ;Include derivative-
                                                     ;specific definitions

            XDEF       Entry, _Startup, main         ;export symbols

            XREF       __SEG_END_SSTACK              ;symbol defined by the
                                                     ;linker for the end of
                                                     ;the stack

;******************************************************************************
;-----------------------------variable/data section----------------------------
MY_EXTENDED_RAM: SECTION

             org  $1000                 ;Start the memory locations at $1000

R1           equ  $1001
R2           equ  $1002
R3           equ  $1003
btn_count    ds.w 1

;******************************************************************************
;-----------------------------code section-------------------------------------
MyCode:     SECTION
main:
_Startup:
Entry:
            lds   #__SEG_END_SSTACK     ; initialize the stack pointer
            cli                         ; enable interrupts

            ldab  #$00
            stab  btn_count             ; set count to 0

            ldaa  #$00                  ; clear register A

            ldaa  DDRH                  ; PTH bit 0 and 3 are inputs
            anda  #$F6                  ; 11110110
            staa  DDRH

            ldaa  DDRB                  ; PTB Bits 0 through 3 as output on LED
            oraa  #$FF                  ; 00001111
            staa  DDRB

            ldaa  DDRJ                  ; Make PTJ output
            oraa  #$02                  ; 00000010
            staa  DDRJ

            ldaa  PTJ                   ; enabled leds ground
            anda  #$FD                  ; 11111101
            staa  PTJ

            ldaa  DDRP                  ; Turn off seven-segment display
            oraa  #$0F
            Staa  DDRP
            ldaa  PTP
            oraa  #$0F
            staa  PTP

;******************************************************************************
;-----------------------------PollSwitches:------------------------------------
PollSwitches:
PollSW2:
            ldaa  PTIH                  ; Check if SW2 (PH3) has been pressed
            anda  #$08                  ; clear all bits except bit 3
            cmpa  #$00                  ; If bit 3 is 0 then SW2 was pressed
            bne   PollSW5               ; Poll for SW5 if not pressed
            bsr   DebounceSW2           ; DebountSW2 because it was pressed
PollSW5:
            ldaa  PTIH                  ; Check if SW5 (PH0) has been pressed
            anda  #$01                  ; clear all bits excpet bit 0
            cmpa  #$00                  ; if bit 1 is 0 then SW5 was pressed
            bne   PollSwitches          ; reset the poll if not pressed
            bsr   DebounceSW5           ; DebounceSW5 because it was pressed
            bra   PollSwitches          ; Forever poll SW2 and SW5

;******************************************************************************
;----------------------------DebounceSW2:--------------------------------------
DebounceSW2:
            bsr   Delay                 ; call delay for software debounce
            ldaa  PTIH                  ; see if SW2 (PH3) has been pressed
            anda  #$08                  ; clear all bits except bit 3
            cmpa  #$00                  ; if bit 3 is 0, Sw2 was pressed
            bne   SW2hi                 ; we branch if SW2 send high signal
            ldab  btn_count             ; making it here means SW2 was pressed
            incb                        ; increment btn_count in Reg A
            stab  btn_count             ; store that value back in btn_count
            ;bsr   LEDCount              ; now figure out what LEDs to light
            stab  PORTB
SW2hi:
            rts                         ; return

;******************************************************************************
;----------------------------DebounceSW5:--------------------------------------
DebounceSW5:
            bsr   Delay                 ; call the delay for software debounce
            ldaa  PTIH                  ; see if SW5 (PH0) was pressed
            anda  #$01                  ; clear bits except bit 0
            cmpa  #$00                  ; if bit 1 is 0 then SW5 was pressed
            bne   SW5hi                 ; we branch if SW5 sends a high signal
            ldab  #$00                  ; SW5 was pressed, clear btn_count
            stab  btn_count
            stab  PORTB
            ;bsr   LEDs_OFF              ; branch to turn off all LEDs, restart
SW5hi:
            rts                         ; return

;******************************************************************************
;----------------------------LEDCount------------------------------------------
LEDCount:
            ldaa  btn_count             ; check if btn_count is 1
            cmpa  #$01
            bne   Light2                ; branch for next count if not
            ldaa  PORTB                 ; if btn_count is 1, turn on first LED
            oraa  #$01
            staa  PORTB
            bra   Finished              ; all done for a 1 count
Light2:
            ldaa  btn_count             ; check if btn_count is 2
            cmpa  #$02
            bne   Light3                ; branch for next count if not
            ldaa  PORTB                 ; if btn_count is 2, light up 2 LEDs
            oraa  #$02
            staa  PORTB
            bra   Finished              ; all done for a 2 count
Light3:
            ldaa  btn_count             ; check if btn_count is 3
            cmpa  #$03
            bne   Light4                ; branch for next count if not
            ldaa  PORTB                 ; if btn_count is 3, light up 3 LEDs
            oraa  #$04
            staa  PORTB
            bra   Finished              ; all done for a 3 count
Light4:
            ldaa  btn_count             ; check if btn_count is 4
            cmpa  #$04
            bne   Finished              ; ignore if not a 4 count
            ldaa  PORTB                 ; if btn_count is 4, light all 4 LEDs
            oraa  #$08
            staa  PORTB
            bra   Finished              ; Finished with LEDCount
Finished:
            rts                         ; return

;******************************************************************************
;----------------------------LEDs_OFF------------------------------------------
LEDs_OFF:
            ldaa  PORTB                 ; turn off the 4 LEDs (PB0 - PB3)
            anda  #$F0
            staa  PORTB
            rts                         ; return

;******************************************************************************
;-------------------------------Delay:-----------------------------------------
Delay:
            psha                        ; save register A on stack
            ldaa  #150                  ; this value determines delay length
            staa  R3
L3          ldaa  #10
            staa  R2
L2          ldaa  #240
            staa  R1
L1          nop                         ; 1 Intruction Cycle
            nop                         ; 1
            nop                         ; 1
            dec   R1                    ; 4
            bne   L1                    ; 3
            dec   R2                    ; Total = 10 cycles
            bne   L2
            dec   R3
            bne   L3
            pula                        ; restore register A
            rts

;******************************************************************************
;---------------------------Questions------------------------------------------
; 1) Why is debouncing important?
;    Debouncing is important because in modern digital systems, the processors
;    are so fast that bounce-back due to the mass of the mechanical switch 
;    causes noise in the system registering multiple button presses when only
;    one is desired.
;
; 2) How can I debounce in hardware?
;    Analogues to a software delay technique a hardware delay technique could
;    involve an R-C circuit that exploits the time constant found in capacitors
;    to drive the time delay needed to wait out the bounce-back from a
;    mechanical switch.
;
; 3) What other electro-mechanical device might bounce?
;    An electro-mechanical relay would be an example of a device that might
;    bounce since it has metal conacts and thus mass. Also because its on a
;    moveable strip of metal it has springiness.
;
; 4) List the number of cycles for each of the opcodes used in your delay 
;    function, then sum the total time of the delay in clock cycles.
;    (1/24MHz)*10*240*150 = 15ms