PElabs help

Vern

Forgive me if this is the wrong place for this to be posted but I really need some help wrapping my head around whats happening in this code example in the book. The example code isn't commented and I can't figure out how it works, if someone could just step through it and explain what it is each line is doing and how it ends up creating a 3hz blink I would be very thankful.

'' AnotherBlinker.spin

PUB Blink | pin, rate, reps

    pin := 4
    rate := clkfreq/3
    reps := 9

    dira[pin]~~
    outa[pin]~
    
    repeat reps * 2
       waitcnt(rate/2 + cnt)
       !outa[pin]

I understand that
pin := 4 sets the variable pin to pin 4
rate := clkfreq/3 sets the rate variable to a 3hz frequency
reps := 9 obviously sets the variable reps to 9

dira and outa I get one is set to output the other set to an off or 0 state

Its the repeat loop I don't get.

Ok so the repeat loop loops 18 times correct.

Each loop it waits for 1.5 seconds before performing
!outa[pin]

!outa[pin] sets the pin4 to high but then it loops back around immediately to the waitcnt.

Wouldn't that make the blink to fast to see? Does !outa[pin] change the actual value stored by pin or does it simply output the opposite of what is stored in pin?

If it assigns a new value to pin4 then loops and waits a half second again that would explain the blink rate.

If it doesn't assign a new value to pin4 then why can I see the blink?

I'm confused and this is probably face slappingly simple but I could use a bit of guidance here.

Ron Czapala

The !outa[pin] is toggling the pin (from high to low or low to high) on each loop - thus causing an attached LED to blink.

Vern

So it toggles it and holds that state through the next waitcnt until it is toggled again?

Thank you for the quick response.