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1. (Department of Electronics and Information Engineering, Jeonbuk National University, Jeonju 54896, Korea {wes7845@naver.com, felipe.p.vista.iv@gmail.com} )
2. (Advances Electronics & Information Research Center, Jeonbuk National University, Jeonju 54896, Korea )

GPS working set, ECU, ISO 11783, CAN bus, Virtual terminal, Precision agriculture

## 1. Introduction

Microprocessors (MPUs) and microcomputers are manufactured by a wide range of vendors, and electronic control units (ECUs) equipped with MPUs are installed in vehicles. A network and communication bus connect measuring and control units. Until recently, it has been difficult for these interconnected components to exchange information due to MPUs’ different internal structures and operation principles. To address this problem, standardization of computer communication has been actively pursued, and one example has been set up by the Society of Automotive Engineers (SAE) and the International Organization for Standardization [1].

The evolution of agriculture has led to uncertainty in production and instability in both supply and demand. To address such problems, extensive research has been conducted on mechanization and automation over the past 20 years. As a result, up to 80 percent of agricultural machines on the market include precision-agriculture components. The term precision agriculture'' (also known as precision farming) was officially adopted at an international conference in June 1997 at the University of Minnesota, USA [2]. In one study, Ünal proposed the integration of ZigBee communication and a controller area network (CAN) bus to reduce wire usage in precision farming [3].

Farmers are able to use a variety of systems economically and easily thanks to integrated management systems that monitor and analyze data to control farming equipment and implements. One such system is the Farm Management Information System (FMIS), which calculates the draft forces needed for pulling an implement to determine tractor power requirements and corresponding fuel consumption [4]. Another is an Agricultural Process-Data Service (APDS) prototype, which is part of the infrastructure in information-driven production [5]. Yet another type is an information management system for automated operation of a tractor-implement setup for managing information relevant to a task at hand [6]. An integral component for each of these systems is working sets, which consist of ECUs that handle data gathering and transmission.

In this study, a GPS ECU was designed for receiving and processing GPS data so that a tractor can receive and process essential GPS data. The algorithm structure is shown in Fig. 1. An analysis of experimental data shows that the implemented embedded system for the GPS working set complies with the required standard. The communication process was successfully implemented while providing the required GPS data. Plug-and-play functionality is also available, even if machines and implements may originate from different manufacturers and countries.

The contributions of this study are as follows:

· An ISOBUS compliant GPS working set

· Plug-and-play functionality regardless of farm-equipment source

· A device that is not specific to Global Navigation Satellite Systems (GNSSs) that can be used with any system that uses the standard data format of the National Marine Electronics Association (NMEA)

· Implementation of ISOAgLib in an embedded system

The proposed working set is presented in Section 2, followed by a description of the working set components in Section 3. The resulting system is then presented in Section 4, followed by a discussion in Section 5 and then the concluding remarks.

Fig. 1. Algorithm structure of proposed agricultural GPS ECU example.

### 1.2 Related Works

Tractors are the most common mechanical equipment used in modern agriculture and are powerful prime-mover work vehicles. The interface between a tractor and a farm implement is crucial since the tractor usually powers the implement in addition to controlling the work being done, whether stationary or in motion. A robust interface facilitates the task of connecting agricultural machinery or implements from one manufacturer to a tractor produced by a different manufacturer.

The advantage of this interface is that it makes mounting agricultural machinery and implements from different manufacturers a relatively straightforward process. Ultimately, farmers will be able to make a variety of choices, while manufacturers will benefit from the development of innovative products. However, until recently, it has been very difficult to use electronic systems in everyday farm works due to the absence of any standard for interfacing the electronic systems of a tractor with those of implements from other manufacturers.

This need has led to the formulation of the international standard ISO 11783, Tractors and machinery for agriculture and forestry — Serial control and communications data network'' [7,8]. ISO 11783 has been developed and now extends beyond the signal interface to virtual terminals, file servers, diagnostic interfaces, work area controllers, and domains. Although there are numerous manufacturers of agricultural machinery in Korea, only a few companies develop and produce ECUs that are compliant with the ISO 11783 protocol. For this reason, this research was carried out to address the important need to develop an ECU for agricultural machinery in Korea that complies with ISO 11783 [8].

Pereira $\textit{et al}$. worked on remote access to a CAN-based distributed control system (DCS) using several computers with ECU VTs, which use the IsoAgLib open library [9]. Backman $\textit{et al}$. discuss the use of ISO 11783 in the combined navigation and control of a tractor and an implement. They reported that the ISO 11783 network can transmit and receive all measurement data and control signals [10]. Oksanen $\textit{et al}$. presented a method of providing a development and run-time environment for designing an embedded system controller for a tractor and implements that is ISO 11783 compatible through software integration [11].

Sarker $\textit{et al}$. designed an embedded system ECU that uses GPS with IAR and IsoAgLib for agricultural tractors and follows the most important requirements of ISO 11783 [12]. Ham $\textit{et al}$. developed hardware and software aspects of GPS, light control, and sprayer ECUs according to the ISOBUS standard via the IsoAgLib library [13]. Stoll developed a CAN data logger system called SCANGate for recording auxiliary sensor data. It integrated several components, including an ECU, through messages transmitted over the tractor’s ISOBUS [14].

Rijanto’s logger went a bit further with a real-time maintenance embedded system that communicates with other ECUs through a CAN bus, which are then recorded to a secure digital card and then sent to an internet of things (IoT) server [15]. It must be noted that IoT entails the utilization of online systems security aspects [16].

GNSSs use satellites to calculate the position, elevation, and velocity of moving objects around the globe. They include a wide range of systems, including GPS (USA), GLONASS (Russia), Galileo (Europe), and Beidou (China). GPS data are an essential component of many applications, including simultaneous localization and mapping (SLAM) [17], autonomous driving [18], and heading for navigation [19].

## 2. Proposed Working Set Design

We will begin by describing the software and hardware implementation of GPS data for enabling precision agricultural equipment to perform CAN communication (CAN bus) using the ISOBUS 11783 protocol. Communication between different types of agricultural equipment and implements using the ISOBUS 11783 protocol is also analyzed to verify the effectiveness of the proposed method. The hardware development environment for the GPS working set is provided in Fig. 2.

The ARM version of IAR Embedded Workbench was used as the development environment for implementing GPS ECUs, and an STM32F107 ARM 32-bit Cortex-M3 board was used for the ECU hardware. A CAN bus was used for communicating via ISOBUS, and the UART communication function was used for retrieving data from the GPS receiver. In addition to ISOAgLib, the virtual terminal required a new library that included APIs to provide additional functionality.

Tractors and machine implements that comply with the ISO 11783 standard transmit and receive messages via CAN communication. All the interconnected ECUs communicating via CAN inside agricultural machines are microcontroller devices with a design based on international-standard computer network protocols and CAN bus standards. For the purposes of this study, the GPS working set was designed and implemented using the open-source ISOAgLib library, which is based on the ISO 11783 standard. The ISOAgLib library is an essential component in the development of an ISOBUS protocol-compliant GPS ECU. The GPS working set consists of a master and one member. The GPS ECU acts as the controller for the set member and complies with the ISO 11783 standard when transmitting position and time data to the CAN bus. The procedure for developing an ISOAgLib-based GPS working set is shown in Fig. 3.

Fig. 2. Hardware setup.

Fig. 3. Development process.

## 3. Working Set Components

### 3.1 ISOBUS

The International Organization for Standardization has merged SAE 1989 and DIN 9683 to establish ISO 11783 (ISOBUS). ISO 11783 describes an international standard data communication protocol and bus based on CAN2.0B. It is derived from a document from the Society of Automotive Engineers (SAE), J 1939, and was developed jointly for trucks, buses, construction, and agriculture [1].

The purpose of ISO 11783 is to provide an open and interconnected system for onboard electronic systems that enables ECUs to communicate with each other via a standardized system. The main components of the ISO 11783 standard that play an important part in the design of the working set are the physical layer [20, p. 2], datalink layer [21, p. 3], network layer [22, p. 4], virtual terminal [23], implement-messages application layer [24], tractor ECU [25], task controller and management information system data interchange [26], file server [27], and diagnostic services module [28]. Tractors and implements that comply with the ISO 11783 standard transmit and receive messages via the CAN specification, by which ECUs are interconnected to the CAN bus. They contain micro-controllers and devices that are compliant with the international standard for the computer network protocol and bus standards.

Fig. 4. VT-Designer.

### 3.2 ISOAgLib

Spangler and Wodok [7] have utilized an application development methodology using ISOAgLib. Tumenjargal [13,29,30] and Sarker [12] have conducted research on the development of ECUs that can be used in precision agricultural machinery, drawing on Spangler and Wodok’s application development methodology. The ISOAgLib library, which includes the vast ISO 11783 standard protocols, is an essential component in the development of GPS ECUs based on the ISOBUS protocol [25]. It is an open-source programming library that includes all of the functions built into the communications system in accordance with standard ISO 11783, including the user interface, virtual terminals, or task controllers [1, p. 1].

The ISOAgLib library consists of several parts, including communications, a scheduler, driver extensions, a hardware abstraction layer (HAL), and hardware drivers. All functions involving the compliance of machine interface and functions with standard protocols are already implemented in ISOAgLib, making it easier to develop ISOBUS applications. ISOAgLib is currently in active use in fields such as agriculture, forestry, construction, and special vehicle systems. Conveniently, an API (application programming interface) for an ECU has already been developed that uses the ISOAgLib library [12,31].

For the present study, each soft key was configured to correspond with information from the GPS, ECU, and firmware so that each key could be allocated its corresponding Data Mask and be properly displayed in the virtual terminal. In the case of data from ISOAgLib, both a CAN server and a VT client-server PC version were required to utilize ISOAgLib. In this study, however, programs were coded to enable implementing ISOAgLib in an embedded system.

### 3.3 XML Object Pool

A file in an IOP format (ISO 11783 ObjectPool) is required when the Cortex-M3 ARM-based ECU API is configured. The file includes library files with various functions in the data mask of the virtual terminal. The ISOAgLib library examples include XML files that are needed to create *.IOP files. These XML files need to be modified to customize the data mask with additional buttons, soft keys, and graphics to be included in the VT data mask.

The IOP file can be obtained from vt2iso.exe'' as provided by ISOAgLib, as well as the library files (*.inc, *.h) required to create applications. The XML file for IOP production is created using markup language. Users unfamiliar with XML may encounter some difficulty when writing code, but the task is made easier by VT-Designer, whose graphical interface enables object pools to be organized visually.

Lastly, ISOAgLib can also be used to create API and IOP files for desired functions to be implemented in the ECU. These functions are the parts of the application that transmit longitude and latitude coordinates and time data from the GPS to the GPS parser and then the VT. The design process using VT-Designer is shown in Fig. 4. It is possible to create an XML file and configure files in IOP format using the drag-and-drop feature of VT-designer.

### 3.4 CAN Communication

There are three separate CAN standards: CAN 1.0, 2.0A (standard CAN), and 2.0B (extended CAN). The main difference between them is the length of the identifier prepended to each message. Version 2.0B extended frames contain a 29-bit message identifier (Bosch, 1991). More information on CAN buses is available from Bosch (1991).

The CAN communication flow consists of large texts that provide the content of CAN messages and small text that provides PGN CAN message data with a size of 8 bytes. The VT status message is sent first with a PGN of E600 and a control byte of FE. This is omitted after the first message since the CAN bus protocol requires messages to be transmitted at a rate of once every second. The VT’s time/date (TD) message has a PGN of FEE6 and is transmitted continuously to all ECUs. Next is the address claim, in which each ECU claims ownership of an assigned address. If an ECU’s address is a duplicate of another’s, the working-set master with lower priority modifies its address according to the ISOBUS protocol. After receiving the PGN (EA00, 00EE00) through which address claims are conducted, each working-set master checks its own address and then displays the number of its members (FE0D, 01...).

Fig. 5. Experimental Setup.

Fig. 6. ECU-VT communication by CAN Analyzer.

## 4. Implemented System

Experimental and analytical data confirmed that the embedded GPS working set system observes the standard communication protocol when successfully transmitting the GPS data required by an agricultural machine. Standard time and position data were supplied separately to connected farm implements to perform precision agriculture tasks efficiently. The system architecture of the GPS working set has demonstrated its overall applicability to agricultural work. The system also complies with standard protocols for plug-and-play functionality for manufacturers from various countries, which is an additional convenience for users.

### 4.1 Experimental Setup

The experimental setup for the proposed system is shown in Fig. 5, where a uBlox M8 GNSS EV kit (EVK-M8T) was used as a GPS receiver with an ARM Cortex-M3 used as the controller for the system. CAN messages were analyzed using the KVASER PCIEcan HS, and an IntelliView IV virtual terminal was set as the communication target for verifying the system’s compliance with the ISO 11783 standard.

### 4.2 CAN Analysis

The GPS ECU complies with the VT and ISOBUS protocols, as shown in the CAN communication in Fig. 6. It is difficult to fully understand the message even though it is the actual data transmitted and received since only key information can be seen in the CAN analyzer, not original CAN 2.0B type data [7,12,31]. Hence, the results are presented in a much clearer manner in Fig. 7 as the flow of messages communicated during the experiment.

The analyzed data are presented as a flowchart of the entire communication flow of messages exchanged between the GPS ECU and the VT, beginning with the VT status message and real-time transmission of GPS data. In the flowchart, periodic and unnecessary messages are omitted to clearly show the data transmission/reception between the GPS and VT. The object pool remains in a transfer state until the entire object pool has been successfully transmitted and received via the CAN bus between the commercial VT and the GPS ECU without the GPS receiver. At the same time, the GPS working set with the GPS receiver transmits GPS data to VT.

Periodic and unnecessary messages are also omitted in the CAN message flow chart to show data transmission and reception between the VT and the GPS working-set master. Messages omitted after the initial message are VT status, time/date (TD), and working set maintenance messages. One example of these messages is the cap illumination (CL) message, which is sent from the VT to the tractor ECU (TECU). The CL message concerns the lighting in the driver’s seat. It is transmitted continuously and periodically until a response is received from the VT, but since the TECU is not present on the network, the message will continue to be transmitted.

Fig. 7. GPS ECU and VT CAN Communication Analysis (Detailed explanation of process explained in Sections 4.3 and 4.4).

### 4.3 Working Set

$\textbf{Part I:}$ The GPS working set consists of a working-set master and a working-set member, which comprise the basic units of an ISOBUS protocol working set. PGN (E700, FF ...) is a maintenance message that is sent by the working-set master separately from the VT status message in Fig. 7(a). This message is also omitted after the first message is transmitted to ensure that at least one message per second is transmitted.

The ECU then submits a request for information about which language is being used by the VT (EA00, 0F FE 00) [15]. The language of the VT used for the present experiment was English, so it returned a message (FE0F, 65 6E...) as part of the language command to the GPS working-set master, which indicated that the English setting should be used. Since the current ECU was set to little endian mode, the message was in PGN FEOF format. The first two bytes of the language command message after PGN FEOF refer to language converted to ASCII format (i.e., 65'' for e,'' and 6e'' for n''). The ECU then submits a query and receives information about the number of soft keys, fonts, hardware specifications, and memory requirements.

Fig. 8. Firmware with Korea time.

Fig. 9. Real-time latitude & longitude.

### 4.4 Object Pool Transmission: ECU to VT

When the explained preliminary steps are completed, the entire object pool is divided into ETP messages and transmitted from the ECU to the VT. The ETP sends and receives information regarding the number and size of the packages. ETP messages begin with sequence 1, and the maximum number of ETP packages is set at 30. The second byte of the get-memory message set is the international standard version of ISO 11783, with which the VT is compliant, and the third to the sixth bytes describe the memory requirement.

$\textbf{Part II:}$ The VT currently used is ISO 11783-compliant (second edition of 2010) with a required memory of $\textbf{00 80 FE}$ (hex, little endian) bytes, which is equal to 33,022 bytes. The second to the fifth bytes of ETP.CM$\backslash\_$RTS refer to the number of bytes that will be transmitted ($\textbf{80 89}$ hex; little endian; 32,905 bytes) (Fig. 7(b)).

$\textbf{Part III & Part IV:}$ The object pool of the GPS working set is sent via ETP, and the remaining small capacity is transferred to the VT via TP (Fig. 7(c), Fig. 7(d)). An End of Object Pool ($\textbf{E700}$,12 ...) message is then sent when the object pool transfer is complete.

$\textbf{Part V:}$ When the object pool to transfer to the VT is complete or a soft key is pressed, a corresponding message ($\textbf{E600}$, $\textbf{00}$ ...) is sent to the ECU (Fig. 7(e)). The seventh byte of the soft-key activation message ($\textbf{E600}$, $\textbf{00}$ ...) is a unique code that is assigned to the soft key and defined in the object pool. Three soft keys are activated in the object pool of the current GPS working set. The first (keycode 254) contains information about the current ECU software, the second (key code 255) includes GPS information, and the third (key code 256) is an auxiliary.

$\textbf{Part VI:}$ The GPS working-set master transmits three 15-byte packets and executes TP when the soft-key is released. VT receives a message indicating that TP has been completed when the operation is completed. Strangely, there are notification messages ($\textbf{E600}$, $\textbf{B3}$ ...) indicating that the string values have been updated (Fig. 7(f)). For this response message to be generated, a message that changes string values ($\textbf{E700}$, $\textbf{B3}$ ...) must first be transmitted. This message ($\textbf{E700}$, $\textbf{B3}$ ...) cannot be checked using the CAN bus and is transmitted as an 8-byte data message in the TP.

The data transmitted after the sequence byte ($\textbf{B3 40 9C}$ ...) were examined and verified for CM$\backslash\_$data transmission. $\textbf{B3}$ refers to $\textbf{E700 B3}$ and means the change of a string value (transport protocol), and $\textbf{40 9C}$ is an Object ID $\textbf{40000 i}$n little endian mode. The actual output string for the longitude object ID is 40,000. It can be seen that the output string of the latitude object ID (40001) is changed through the third and fourth data ($\textbf{419C}$) in the subsequent TP.CM$\backslash\_$Data Transfer message.

## 5. Discussion

It is difficult to fully understand the message even though it is the actual data transmitted and received since only key information can be seen in the CAN analyzer, not original CAN 2.0B type data [7,12,31]. The VT screen (Fig. 8) shows when the object pool is uploaded and the first soft-key (key code 254) is pressed. The data mask provides information about the ECU firmware updates, time data, and the second soft-key of the GPS receiver in real time. When the second soft key (keycode 255) is pressed, a new display is shown (Fig. 9).

The object pool’s limitations include memory and creating figure objects. Image data to be processed by the VT-designer can be represented only by a maximum of 8 bytes (256 bits). As shown in Fig. 9, the bitmap image uploaded to the VT has a lower resolution than the original, making it difficult for the image to display map data. It is difficult for ECU hardware with 256K of flash memory to accommodate even this low-resolution image data. Replacing the ECU with better hardware may be a workaround but is not a long-term solution. A better solution may be to ensure that there is a large amount of map data in the VT. Once this problem has been solved, the GPS ECU should require no further hardware configuration, and neither flash memory nor map resolution will be an issue.

There is currently an abundance of high-precision agricultural GNSS receivers and modules on the market to choose from. The designed ECU is not GNSS-specific as long as it can receive and process the GPS data that is eventually transmitted to the virtual terminal. The ECU is designed to process agricultural data by making use of GPS data, and the utility of the design method has been confirmed by experimental communication with a virtual terminal. The GPS ECU $\textbf{processes}$ longitude, latitude, and universal time-coordinated (UTC) data inputs from the GPS receiver and is responsible for CAN communication for the VT and related data transmission such as position, time, and bearing.

## 4. Conclusion

This paper has dealt with the design and implementation of an embedded system GPS working set based on the ISOBUS protocol for autonomous agricultural equipment, particularly for South Korea. Experimental analysis confirmed the successful communication between a VT and GPS ECU and implementation of plug-and-play functionality. Object-pool transmission, ECU response to VT commands, modification of the VT data mask, and analysis of transmitted and received messages during communication via the CAN analyzer have been discussed.

The GPS working set is only responsible for interworking, transmitting, and updating the VT for GPS-receiving data. In the case of farm equipment that is compliant with the ISOBUS protocol, a functional GPS working set in which plug-and-play functionality is executed is sufficient, regardless of the country and manufacturer. Since every manufacturer uses different hardware and software, a VT may not always be available, but GPS data alone is useless to farmers unless the user has access to a visual display of a map database. Therefore, future research on VT display of GPS data based on map data is an essential prerequisite to developing a fully functional precision agricultural GPS system.

### ACKNOWLEDGMENTS

This work was supported in part by the Brain Research Program of the National Research Foundation (NRF) funded by the Korean government (MSIT) (No. NRF-2017M3C7A1044816) and in part by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (No. 2019R1A6A3A01094685).

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## Author

##### JaYu Kim

JaYu Kim received his Master Degree in Electronic engineering from Jeonbuk National University, Jeonju, Korea, in 2017. His research interests are in the areas of Precision agricultural machinery, International standard protocol, Sensor fusion, Sensor network, Flying control & Optimization.

##### Felipe P. Vista IV

Felipe P. Vista IV got his Ph.D. degree in Electronic Engineering from Jeonbuk National University, Jeonju, Korea in 2013. He is a Research Assistant Professor fellow for Advances Electronics and Information Research Center and concurrently a lecturer at School of International Science and Engineering for Global Frontier College of JBNU. His research interests are in the field of Systems Design, Software Development, Fuzzy Logic, Sensor Fusion, Embedded Systems, Navigation Systems, Marine Information System, Signal Processing & Augmented Reality.

##### Dae-Young Lim

Dae-Young Lim got his Ph.D. degree in Electronic Engineering from Jeonbuk National University, Jeonju, Korea in 2018. Currently He is a post-doctoral fellow in Department of Electronic Engineering, Jeonbuk National University. His research interests include automatic control, neural networks and artificial intelligence.

##### Kil To Chong

Kil To Chong received the Ph.D. degree in Mechanical Engineering from Texas A&M University, College Station, USA in 1995. Currently, he is a Professor at the School of Electronic Engineering, Jeonbuk National University, South Korea and head of the Advanced Research Center of Electronics. His research interests are in the areas of Sensor network, Network system control, Motor fault detection, Time-delay systems, Neural network, Machine Learning, Artificial intelligence, and Bioinformatics.