Enhancing the Modbus Communication Protocol to Minimize Acquisition Times Based on an STM32-Embedded Device

Abstract

The primary function of a distributed bus is to connect sensors, actuators, and control units that are used for an acquisition process. Application domains, such as industrial monitoring and control systems, manufacturing processes, or building automation, present different requirements that are not exactly invariable and coherent. Updating data from Modbus-type devices involves updating data through a technique called polling, which involves repeatedly scanning the registers from each device. This paper highlights the performance of Modbus communication, considering scenarios in which distributed devices are integrated and accessed registers are or are not at consecutive addresses. The Modbus protocol allows reading one or more holding-type data registers. If the registers are not at consecutive addresses, multiple requests are required, with implications for the real-time characteristics of the data acquisition system. We studied the data update times within the SMARTConvert application when variable numbers of registers are accessed, and we designed an extension for the Modbus protocol. The major reason Modbus is used in current research is that no assumptions are required about application semantics, and the performance/resource ratio for generic services is excellent.

Communication Time Optimization of Register-Based Data Transfer

“…The concept of improving performance through various ways of grouping registers was mentioned in articles [6][7][8][9][10][11][12]. The contributions of each one are briefly summarized below.…”

“…Gȃitan and Zagan, in their work [9,10], discussed the performance of Modbus communication in various scenarios. They analyzed the impact of accessing multiple registers with consecutive or separated addresses.…”

“…Each register is assigned to exactly one frame (8). The lower and upper bounds of the frames, i.e., r i and r i , are constrained by the registers assigned to them in ( 9) and (10). Frame sizes are bounded from below by the assigned registers (11) and bounded from above by 1 or s, according to the values of l i (12).…”

Modbus Extension Server Implementation for BIoT-Enabled Smart Switch Embedded System Device

“…Compared with the previous publication [ 22 ], the server module proposed in this paper is a novelty because it is the first ModbusE (MBE)-based implementation integrated into an SH. The system required the implementation of the Modbus RTU protocol at BIoT (smart switch) server stations, respectively, as well as the completion and definition of new requirements for the Modbus protocol extension called ModbusE at the MBE_RTU server station level with 100% compatibility with the maintained Modbus RTU protocol [ 23 ]. The STM32F429I-DISCO microcontroller development kit, the STM IDE Cube application development tool, and the FreeRTOS operating system were used for laboratory modeling and experimental testing, presenting an example of ModbusE and IoT-based SH usage.…”

“…When the current device sends the response on the bus, if the slot address does not match the device's ModbusE address for the corresponding response slots, the myTaskServerMBEcycle task moves the data from the application memory organized by Modbus data and addressing model into the slot with the function "void vexecuteRecvSlotWriteRegs(uint8_t SlotIndex)" given the Modbus read functions 1, 2, 3, 4, 7, 11, 23 based on the information in the MY_SLO_PARAM slot structure. For slots with Modbus APDU, i.e., when the slot address matches the Modbus address of the device, the myTaskServerMBEcycle task moves the data and responds if necessary according to the Modbus specifications for functions 1,2,3,4,5,6,7,11,15,16,22,23, directly using the information in the request with the function "void vModbusExecuteFunctions(void)". As the highest priority task, it will perform atomic read/write operations.…”