xdef        pgstart
            absentry    pgstart
*
*******************************************************************************
* Macros
*

PORTB       equ         $0001
DDRB        equ         $0003

SCHBDH      equ         $00C8
SCHBDL      equ         $00C9
SCICR2      equ         $00CB
SCISR1      equ         $00CC
SCIDRL      equ         $00CF

CRGFLG      equ         $0037
CRGINT      equ         $0038
RTICTL      equ         $003B

*
*******************************************************************************
* RTI Vector Section: [ $FFF0 to $FFF1 ]
*

            org         $FFF0
            dc.w        RTIISR

*
*******************************************************************************
* Data Section: [ $3000 to $30FF ]
*

            org         $3000

counter     dc.w        $0000

msg         dc.b        'This program will print a $ every second',$00

numBuf      ds.b        $0002
            dc.b        $00

inNumBuf    dc.w        $0000

*
*******************************************************************************
* Program Section: [ $3100 to $3FFF ]
*
            org         $3100

pgstart
            lds         #pgstart

            ldaa        #1
            staa        SCHBDH

            ldaa        #$0C
            staa        SCICR2

            ldaa        #%00011001
            staa        RTICTL

            bset        CRGINT,#%10000000
            bset        CRGFLG,#%10000000

            ldx         #msg
            jsr         printmsg

            cli

loop        jsr         getchar
            tsta
            beq         loop
            jsr         putchar
            bra loop

;******************************************************************************
; Subroutine Section
;

RTIISR      bset        CRGFLG,#%10000000
            ldx         counter
            inx
            stx         counter
            cpx         #400
            bne         RTIDONE
            ldx         #0
            stx         counter
            ldaa        #'$'
            jsr         putchar
RTIDONE     rti

getchar
            brclr       SCISR1,#%00100000,empty
            ldaa        SCIDRL
            rts
empty       clra
            rts

PrintTwoDigitDecimal
            pshx
            pshd
            pshy
            ldy         #numBuf
ConvertLoop ldx         #10
            idiv
            cpd         #0
            beq         CheckX
XNotZero    addb        #'0'
            stab        1,y+
            exg         d,x
            bra         ConvertLoop
CheckX      cpx         #0
            bne         XNotZero
            ldx         #numBuf
            jsr         printmsg
            puly
            puld
            pulx
            rts

ReadTwoDigitDecimal
            pshx
            pshd
            pshy
            ldd         #0
            ldab        1,x+
            beq         ReadDone
            cmpb        #'0'
            blt         ReadDone
            cmpb        #'9'
            bhi         ReadDone
            pshb
            ldd         inNumBuf
            ldy         #10
            emul
            std         inNumBuf
            pulb
            subb        #'0'
            ldy         inNumBuf
            aby
            sty         inNumBuf
            bra         ReadLoop
ReadDone    puly
            puld
            pulx
            rts

putchar
            brclr       SCISR1,#%10000000,putchar
            staa        SCIDRL
            rts

printmsg
            pshx
            psha
printLoop   ldaa        1,x+
            beq         printDone
            jsr         putchar
            bra         printLoop
printDone   pula
            pulx
            rts

;
;******************************************************************************

            end