Hi Norberto:
Yes, waiting on event bit is a blocking call. Any task can set or clear bits event field, or interrupt service routine can also set or clear bits. once the condition specified to unblock is being met, the task state will change from blocked to ready, and the scheduler will be called to see whether a context switch should be done.
Please refer to the following demo for lwevent usage.
C:\Freescale\Freescale_MQX_4_2\mqx\examples\lwevent
Regards
Daniel