HKJ-lygte:
The LEDs needs very fast pulses at less than 1us in width, variations in the width defines if it 0 or 1. One chip needs 24 pulses, that is the same as 24 bits (8 for each color). When you have more chips in series you need more pulses, 24 for each chip. That means with 10 led you need to generate 240 pulses each better than with us precision.
The datasheets for each chip lists the precise timing requirements, but is is usual about 400 and 800us for 0 and 1, the low uses the opposite time, but is usually not very critical. To signal the end of bits you simply hold the dataline low for some time (50us) and all the chips will update the led output.On the Atmega chips it is fairly tricky to write the code because it can only do up to 16 assembler instructions in a us, on faster processor it gets easier, but watch out for interrupts!
Thank you, I am now fully understand it