itch.io

You could slow it down by creating a counter and then use the counter to time a latch with the most significant bit tied to the data, so that it is turned on and off as a square wave. You'd still be tied to the refresh rate, but you could use that to easily drive a power of two slow down rate. With a more complicated timer you wouldn't have to limit yourself to powers of two and the latch isn't completely necessary, but it would be the "right way."