; William Lark, Jr.
;
; How to make something that makes almost anything   Spring 04 
; hola_Will.asm
; ref - Neil Gershenfeld CBA MIT 2/14/04
; edited by Will Lark "How to make..."  MIT 3/6/04
; AVR hello world program
;

.include "tn15def.inc"
.equ txpin = PB3; transmit pin
.def bitcnt = R16; bit counter
.def temp = R17; temporary storage
.def temp1 = R18; temporary storage
.def txbyte = R19; data byte

.cseg
.org 0
rjmp reset

;
; Place the Text  "plctext"
; assumes no line driver (doesn't invert bits)
;
.equ sb = 1; number of stop bits
plctext:
   ldi bitcnt, 9+sb; 1+8+sb
   com txbyte; invert everything
   sec; set start bit
   plctext0:
      brcc plctext1; if carry set
      sbi PORTB, txpin; send a '0'
      rjmp plctext2; else	
   plctext1:
       cbi PORTB, txpin	; send a '1'
       nop ; even out timing
   plctext2:
       rcall slowbit; one bit delay
       rcall slowbit
       lsr txbyte; get next bit
       dec bitcnt; if not all bits sent
       brne plctext0; send next bit
   ret;
;
; Slow down the bit speed  "slowbit"
;
; 1 MHz crystal: 9600 bps - b=14, 19200 bps - b=5, 28800 bps - b=2
;
.equ b = 16
slowbit:
   ldi temp, b
   bitloop:
      dec temp
      brne bitloop
   ret
;
; Sow down the text "slowtext"
;
.equ delay = 200
slowtext:
   ldi temp1, delay
   charloop1:
      ldi temp, delay
      charloop0:
         dec temp
         brne charloop0
      dec temp1
      brne charloop1
   ret
;
; main program
;
reset:
   sbi PORTB, txpin; init comm pin
   sbi DDRB, txpin
   loop:
      ldi Txbyte, 'H'
      rcall plctext
      ldi Txbyte, 'o'
      rcall plctext
      ldi Txbyte, 'l'
      rcall plctext
      ldi Txbyte, 'a'
      rcall plctext
      ldi Txbyte, ' '
      rcall plctext
      ldi Txbyte, ' '
      rcall plctext
      rcall slowtext
      rjmp loop