A Design of A Modbus Application Protocol for Multiple SCU Connections

다중 제어 장치 연결을 위한 Modbus 응용 Protocol 설계

  • Song, Jeong-Ho (Division of Computer Engineering, Kongju National University) ;
  • Kim, Bo-Hun (Division of Computer Engineering, Kongju National University) ;
  • Kim, Hwang-Rae (Division of Computer Engineering, Kongju National University)
  • 송정호 (공주대학교 컴퓨터공학부) ;
  • 김보헌 (공주대학교 컴퓨터공학부) ;
  • 김황래 (공주대학교 컴퓨터공학부)
  • Received : 2018.01.24
  • Accepted : 2018.04.06
  • Published : 2018.04.30


The Modbus protocol is the most widely used protocol for connecting multiple slave control units (SCUs) in the master control unit. However, the Modbus protocol does not identify which SCU response message corresponds to the service request message. Therefore, when using the Modbus protocol, one service request message can be transmitted after processing the previous message. In this paper, we propose a Modbus application protocol with an index code and a service code to solve the problem. As a result of experimentation, it is possible to transmit the next service request message without processing the previous service request message. And when a communications error occurs, it is possible to identify what type of error occurred using an error detection algorithm. Also, with simultaneous multiple service requests, the proposed protocol can improve processing time by about 66.2%, compared to the original Modbus protocol.


IoT;Master-Slave Communication;Modbus;Protocol;Remote Control


  1. Soo Jeong, Jong Jin Lee, Won Ki Jung, "A Indoor Management System using Raspberry Pi," Journal of the KAIS, vol. 17, no. 9, pp. 745-752, 2016. DOI:
  2. Martin Wollschlaeger, Thilo Sauter, Juergen Jasperneite, "The Future of Industrial Communication: Automation Networks in the Era of the Internet of Things and Industry 4.0," IEEE Industrial Electronics Magazine, vol. 11, no. 1, pp. 17-27, 2017. DOI:
  3. DaeHeon Park, "A Study on Integrated Operation Systems of Plant Factory based on Internet of Things," Ph.D Thesis, SunChon University, 2015.
  4. Bo-Hun Kim, "A Design and Implementation of PC-based Control System for Efficiency Improvement of Industrial Equipments," Ph.D Thesis, KongJu University, 2017.
  5. Jeyasingam Nivethan, Mauricio Papa, "A SCADA Intrusion Detection Framework that Incorporates Process Semantics," ACM CISRC '16 Proceedings of the 11th Annual Cyber and Information Security Research Conference, 2015.
  6. Sungmo Jung, Jae-gu Song, Taihoon Kim, Yohwan So, Seoksoo Kim, "Design of Idle-time Measurement System for Data Spoofing Detection," Journal of the Korea Academia-Industrial cooperation Society, vol. 11, no. 1, pp. 151-158, 2010. DOI:
  7. Saptarshi Naskar, Krishnendu Basuli, Samar Sen Sarma, "ASerial port data communication using Modbus protocol," Journal of ACM Ubiquity, vol. 2008, no. 1, 2008.
  8. Bo-Heon Kim, Jeong-Ho Song, Hwang-Rae Kim, "A Study on Enhancement of the MOD-BUS RTU Protocol for Multi-Device Connection," Proceedings of the KAIS Fall Conference, 2016.
  9. Modbus Application Protocol Manual V1_1b3: Available From: (accessed Aug, 15, 2017)
  10. SamWon Tech Nova Communication Manual: Available From: (accessed July, 21, 2017)
  11. Kisan System KM60xx Modbus Manual: Available From: (accessed May, 10, 2017)