The process by which a block is activated. Activation signals are received on block activation input ports and genearted on block activation output ports. Generally, activation input and output ports are located on the top and bottom of a block, respectively.

While regular inputs and outputs communicate data from block to block through regular links, activation inputs and outputs are connected by activation links that transmit control information. The activation times associated with an activation signal are a set containing isolated time instants and time intervals. Activation at an isolated time instant is called an event. Activation signals made of events are used to activate discrete-time blocks. Such activations can occur at fixed frequencies or sporadically and can be synchronous or asynchronous.

Activation signals are not always drawn explicitly. They can be propagated through the inheritance mechanism, which the software provides for convenience.