*************************************************************************
* Program 4 HARDFLSH.ASM To flash LEDS (PortB) using hardware delay loop*
* with duration read from switches (PortA)                              *
* Hardware JP2 in, JP4 Optional, JP5 ground, JP6 Vcc                    *
*************************************************************************
*define addresses
PORTA EQU 0     ;Port A (switches)
PORTB EQU 1     ;Port B (LEDs)
DDRA EQU 4              ;Data Direction Register for PortA
DDRB EQU 5              ;Data Direction Register for PortB
COUNT   EQU 5000T       ;Timer clock cycles (base ten)
TSR     EQU $13 ;Timer status register
OCFLAG  EQU 6   ;Bit 6 of status register is compare flag
OCHR    EQU $16 ;Compare register 1 high
OCLR    EQU $17 ;Compare register 1 low
CHR     EQU $18 ;Counter high register
CLR     EQU $19 ;Counter low register

    ORG $50
TICKS RMB 1
    ORG $250            ;Storage for value from switches
START: lda #0           ;set all bits of port A as input
       sta DDRA         ;by setting DDRA to 0
       lda #$FF         ;Port B set to output
       sta DDRB         ;by setting DDRB to all 1's
LOOP:  lda #0           ;As Ports must sink current to turn on
       sta PORTB        ;Zeros set LEDs on
       LDX #$00;        ;Load index with 0 value
       LDA PORTA        ;Load accumulator with switches values
FIND_ONE:
       ASRA
       BCC NOT_FOUND
       INCX
       STX $0060
       JMP CONTINUE
NOT_FOUND:
       INCX
       CPX #$08
       BLO FIND_ONE
CONTINUE:
       jsr DELAY        ;Jump to subroutine delay
       ;lda #$FF         ;Ones set LEDs off
       ;sta PORTB        ;
       ;jsr DELAY        ;Delay again
       bra LOOP         ;Repeat
*
DELAY: LDA $0060                ;Store value;;
       sta TICKS                ;from $0060 ;;
       lda CHR                  ;read current value of counter H
       sta OCHR                 ;store in compare register H
       lda CLR                  ;same for counter low byte
       sta OCLR                 ;store in compare register L
       LDX #$00
       STX $0055                ;clearing $0055
LOOP1:
       LDA NUMBERS,X
       STA PORTB                ;sending values to sevenseg
       lda OCLR                 ;read last low byte of compare register
       add #{COUNT%256T}        ;add low byte of count
       tax                      ;save temporarily in X register
       lda OCHR                 ;read last high byte of compare register
       adc #{COUNT/256T}        ;add in high byte of count plus any carry
       sta OCHR                 ;store Acc in high byte of compare register
       stx OCLR                 ;store X in low byte of compare register

HOLD:  brclr OCFLAG,TSR,HOLD    ;hold until counter = register
       LDX $0055
       INCX
       STX $0055
       CPX TICKS
       BLO LOOP1                        ;repeat until X < TICKS
       rts                              ;return to main program
       END                              ;end of program

*
* Codes for 7 segment display, 0 turns on segment
*
NUMBERS:   fcb   %11000000,%11111001,%10100100,%10110000 ; '0','1','2','3'
        fcb   %10011001,%10010010,%10000010,%11111000 ; '4','5','6','7
        fcb   %10000000,%10010000,%00000100; '8'