; sample program for 6809 assembler
; to show what 6809 assembler actually looks like
;
; program to add two multiple precision operands
; where did I get this from?
;

nbytes  EQU     8

        ORG     $1000      ; start at 1000H

; BCD addition subroutine

bcd     ldb     #nbytes
        ldx     addr       ; load data address
        andcc   #$0FE      ; clear carry bit
next    lda     nbytes-1,x ; start loop
        adca    nbytes-1*2,x
        daa
        sta     nbytes-1*3,x
        leax    -1,x
        decb
        bne     next
        rts                ; end of subroutine

; begin main program
; (uses subroutine 'bcd')
        ORG     $1100      ; main program at 1100H
        lds     #$013f     ; initialise SP
        ldx     temp
        stx     addr
        jsr     bcd
        ldx     #msg       ; get address of string
        jsr     print      ; and print it
        nop
loop    bra     loop       ; loop forever

; dummy routine print
print   rts

; allocate data area
        ORG     $0100
addr    FDB     0
temp    RMB     nbytes
msg     FCC     "multiplication done"
        FCB     $0D,00
        END