I found something in this website for Arduino:
The rows are handled by an ULN2803, an array of darlington transistors. This chip is used to sink the current of the activated row. If every LED in a single row is activated, the current for this row will sum up to 320 mA (16 * 20 mA). Definately too much for a single pin of a microcontroller. The ULN2803 is able to sink up to 500 mA per channel and cheap (about 30 euro cent).
So this ULN will take out the power fast this way it won't overload the pin right? I will need 1 for each DotMatrix right?