Event-triggered sampled-data energy control of a pendulum * *This work was supported by Saint Petersburg State University, (grant 6.38.230.2015) and by Government of Russian Federation, Grant 074-U01. The proof of avoidance of Zeno phenomenon in continuous event-trigger was performed in IPME RAS under support of Russian Science Foundation (grant 14-29-00142). The results for event-trigger with a constant threshold (Proposition 2) was performed under support of the Russian Foundation for Basic Research, Grant 17-01-00102-a