Industrials have been increasingly interested in wireless sensor and actuator networks to monitor and control installations. The recent IEEE 802.15.4 standard has been developed to address vital issues of these networks, such as limited battery power and low processing capabilities. However, the standard does not meet all the requirements of industrial networks. For example, only some of the IEEE 802.15.4 nodes save energy. Also, this standard suffers from beacon frame collisions. In this paper, we describe MaCARI, a deterministic MAC layer protocol which allows all nodes to save energy and avoids the beacon frame collisions. We discuss several optimizations to increase the performance of the protocol or to offer QoS features. We evaluated the main components of MaCARI using a simulation and a prototype on a real hardware platform in order to prove their feasibility.