This paper proposes message scheduling on dedicated time slot of ISA100.11a to satisfy real time property. In this paper, a superframe is designed to accommodate periodic real time (PRT) message, aperiodic real time (alarm) message, and non real time (NRT) message. To do so, a superframe is divided into dedicated time slot (DTS) which is used to send PRT message and shared time slot (STS) which is used to send alarm and NRT message. Then, the schedulability of all PRT-messages in the network is analyzed and clustered into low traffic or high traffic scheduling. The results show that this proposed method is feasible to map PRT message into superframe and multi-superframe. As the consequence, PRT message can be delivered within the deadline. Finally, real time and reliable wireless networked control system can be achieved by applying this proposed method.