RAM    equ 0000h
THIS   equ 0010h
END    equ 0020h
SCSR   equ 2Eh
PORTB  equ 1004h      ; address of PORTB register
  org RAM        
  jmp BEGIN
BEGIN:
  ldab 01h            ; move 1 into register b
  stab [PORTB]        ; light b0

  ldab 03h            ; move 1 into register b
  stab [PORTB]        ; light b0

  bsr DELAY1K
  ldab 00h            ; move 0 into register b
  stab [PORTB]        ; turn off bo
  bsr DELAY1K
  jmp BEGIN

;  ldaa [PORTB]        ; move contents of PORTB into register a
;  ldab [PORTB]    ; 

  rts
DELAY10 equ *               ; 10ms delay @ 2.1 mhz
  pshy                      ; save register y
  ldy 0BB8h                 ; load loop counter into y register
DELAY10LOOP equ *           ; loop counter sync address
  dey                       ; decrement counter 
  bne DELAY10LOOP           ; loop until zero in y
  puly                      ; restore register y
  rts                       ; return to caller
DELAY1K equ *               ; 1000ms delay @ 2.1 mhz
  pshy                      ; save register y
  ldy 0Ah                   ; load 10d into register y
DELAY1KLP equ *             ; loop counter sync address
  bsr DELAY100              ; call 100 ms delay
  dey                       ; decrement register y
  bne DELAY1KLP             ; continue
  puly                      ; restore register y
  rts                       ; return to caller
DELAY100 equ *              ; 100 ms @ 2.1 mhz
  pshx                      ; save register x
  ldx 07530h                ; load loop counter into register x
DELAY100LP equ *            ; loop counter sync address
  dex                       ; decrement register x
  bne DELAY100LP            ; continue
  pulx                      ; restore register x
  rts                       ; return to caller