I've got in mind a project that will involve a couple hundred LEDs that have to be independently controlled. I want to make a clock where the individual seconds, minutes, hours, days of the month, and months of the year are represented by a lit LED. As the LED's representing seconds passes 60 seconds and goes to the next minute, all the "second" LED's go out, one "minute" LED turns on, and the seconds start over with all of them being dark. The process repeats indefinitely and cascades into hours, days, months.
So to my beginner's mind, I'm thinking I need one output pin per led. If that's so, how would I go about controlling a couple hundred? Can you chain processors together?