; LEDblink.asm - M. Covington 2006 
; For ATtiny13. 
; Blinks the LEDs attached to PB0 and PB1. 

.include "tn13def.inc" 

.def temp = R16 
.def temp1 = R17 
.def temp2 = R18 
.def mask = R19 

start: ldi temp,0b00000010
       out PORTB,temp ; initialize port B 
       ser mask 
       out DDRB,mask ; port B all outputs 
blink: 
       ; Delay 0.1 sec (1.2 MHz) 
       ldi temp1,200 ; outer loop count 
L1:    ldi temp2,199 ; inner loop count 
L2:    dec temp2 
       brne L2 
       dec temp1 
       brne L1 
       ; Toggle PB0 and PB1 
       ldi mask,0b00000011 
       eor temp,mask 
       out PORTB,temp 

       rjmp blink 
; End of program

So when I got to Maker Day at Maker Faire yesterday afternoon, I was happy to find that Limor Fried, the founder of Adafruit, was giving a presentation on how to start your own business selling kits. This is a growing business right now, as people look for reasons to teach their kids how to solder, or just want to build a neat device. (Adafruit teamed with the Maker Store to offer the infamous TV-B-Gone kit that garnered a lot of attention at CES this year.)

void setup(){
  pinMode(13, OUTPUT);
}
 
void loop(){
  digitalWrite(13, HIGH);
  delay(500);
  digitalWrite(13, LOW);
  delay(500);
}

First, we configure pin 13 for output by setting a bit in Data Direction Register B. Then we turn pin 13 by setting its bit in PORTB. Then we delay 500 milliseconds by marking the current value of timer0, converted into milliseconds, and letting the counter be incremented repeatedly at each clock cycle and overflowed into ever larger holders until the new value of timer0 represents an elapsed time of 500ms. Next we set the bit for pin 13 in PORTB low to turn the LED off. We do the delay dance again and we're home.