Naseem Ullah
Master’s Thesis Electrical Engineering
Embedded Systems 2014
Master’s Thesis
Implementing and Analyzing Single Edge
Nibble Transmission (SENT) Protocol for
Automotive Applications
Naseem Ullah
This exam work has been carried out at the School of Engineering in Jönköping in the subject area Electrical Engineering. The work is a part of the two-year of Master of Science programme with a specialization in Embedded Systems. The authors take full responsibility for opinions, conclusions and findings presented.
Supervisor:
JTH, Alf Johansson Examiner:
JTH, Prof Shashi Kumar
Scope: 30 ECTS
Reg Nr: JTH-Jönköping 2014
School of Engineering Jönköping University SE-551 11 Jönköping Sweden
are controlled electronically by a number of ECUs (Electronics Control Unit) with the combination of sensor modules. To exchange information between the ECU and sensor modules a number of communication standards are used. The most commonly used standards are CAN, LIN, and PWM etc.
The data transmission between the ECU and sensor modules can be easily es-tablished with a PWM (Pulse Width Modulation) techniques in comparison with CAN or LIN. PWM provide a convenient solution in terms of cost and perfor-mance when the data-rate is upto 10-bits. While for higher resolution data rates its performance are not satisfied. Extra effort is needed to implement diagnostic information for the integrity of data. Also, the accuracy of PWM signal is depen-dent on the noise voltage and channel bandwidth. In 10-bit system a single bit is represented by 4mV which face serious problem in automotive system due to the noise voltage pulses which effect the resolution of the PWM. The alternative solution for safe and high data rate which is more than 10-bit resolution is to used CAN and LIN protocols.Both CAN and LIN have availability of diagnostic modes for an ensured data transmission. Also, their capabilities for interconnecting a number of nodes (sensors-modules) on the same network can significantly reduced the wiring cost. But in automotive a number of systems need to communicate through point-to-point link, and it seem to be too expensive to used CAN and LIN for point-to-point communication because of its development complexity and wiring cost for a standalone system. To overcome these issues and to provide an alternative low cost solution the SAE (Society of Automotive Engineers) devel-oped a 3-wire new digital point-to-point protocol called SENT. SENT (Single Edge Nibble Transmission) Protocol is now an international standard (SAE J2716). SENT is unidirectional point-to-point communication protocol, which can be used for high resolution data transmission between sensor module and ECU. The data are transmitted by sensor module in a series of pulses each pulse is 4-bit (one nibble) long and the data are measured between two falling edges by the receiving module. There are total of nine pulses which defined the SENT frame. The first pulse is called calibration pulse, it is used for compensating to recalibrate all the other pulses in case of transmitter clock deviation, this is the best feature of SENT and can be implemented in the decoder design.
This thesis work focuses on the development of SENT protocol decoder and its signal robustness analysis in comparison with the conventional PWM signal. Our first goal is to developed SENT-Protocol decoder in software on the available
microcontrollers is to check how much memory foot print is used and how much the processor overhead. Two platforms has been used for this purpose. First, two implementation designs prototype were made with fixed-point and floating-point development techniques on the 32 bit platform for SENT decoder. Secondly SENT-decoder were developed with 8-bit platform and compared with the two previous designs to check how much memory foot print is used and how much is the processor overhead. Finally, the signal integrity analysis has been performed for PWM and SENT signal using spice simulation. The purpose is to check the maximum data rate limit that the PWM signal support with out creating any bit error in the transmitted signal. The same data rate is then used for SENT signal to be compared with PWM signal.
SENT CAN LIN PWM PSI5 Nios II DE 2 Board GPIO SOPC Builder ADC DAC SPICE Simulation v
First and foremost I want to thank my supervisor Alf Johansson for his continuous supervision and suggestions throughout this thesis and during my complete Mas-ter’s study. I appreciate all his contributions of time, ideas and his great patience to make my M.Sc. I had a great opportunity of learning so many things from him in the meetings during our discussions.
I would like to thank Professor Shashi Kumar for his continuous support and motivation throughout my master study program. I really appreciate his invaluable time and advises that he gave me during my complete study program.
I would also like to thank all my teachers for their full time support and providing invaluable knowledge during my Master’s study. I had a good time while studying in JTH. I want to thank to JTH and Sweden for providing a beautiful environment and a realistic study atmosphere during my study.
Last but not least, I would like to pay a special thank you to my parents whose moral support and prayers has always been with me.
2.3 LIN frame structure . . . 10
2.4 LIN frame structure . . . 11
2.5 Point-to-Point communication with PWM . . . 12
2.6 PWM signal generation . . . 12
2.7 PWM waveform . . . 13
2.8 CAN nodes connection diagram . . . 13
2.9 CAN bus typical applications in automotive . . . 14
2.10 CAN bus typical applications in automotive . . . 15
2.11 CAN extended frame structure . . . 15
2.12 RTL design of SENT IP . . . 16
2.13 MLX90324 functional block diagram . . . 17
2.14 SENT frame . . . 18
2.15 SENT frame structure . . . 19
2.16 SENT synchronization pulse . . . 20
2.17 Nios II core architecture . . . 21
2.18 Different Cores of Nios II Processor . . . 22
2.19 Block Diagram of DE2 Board . . . 23
2.20 PIC18F67J50 Development Board [1] . . . 24
2.21 PIC18F67J50 64-Pins Package . . . 25
2.22 PIC18F87J50-Microcontroller Family Member [2] . . . 26
2.23 A typical output buffer equivalent circuit . . . 27
2.24 Some typical automotive sensors . . . 28
2.25 Position/Speed Sensor Construction . . . 29
2.26 Thermistor Circuit Diagram . . . 31
2.27 Engine Coolant Sensor . . . 31
2.28 TEL4998 Linear Hall Sensor . . . 32
3.1 Automotive electronics systems classifications with respect to SAE classes [3] . . . 36
3.2 Automotive protocols comparison based on their data rates [3] . . 37
4.1 System Development research method . . . 42
4.2 SENT-Receiver and Transmitter . . . 44
4.3 DEV PIC18F67J50 Board [1] . . . 45
4.4 SENT- Transmitter (Sensor) Module . . . 46
4.5 Sensor Oscilloscope output . . . 46
4.6 Complete Frame Timing Diagram . . . 47
4.7 Structure of Status Pulse . . . 48
4.8 Pulse shape . . . 49
4.9 Frame Structure of Short serial message . . . 51
4.12 System Hardware Architecture . . . 53
4.13 System configuration in SOPC-Builder . . . 54
4.14 Data Types of C-Language [4] . . . 55
4.15 Detection of Synchronization Pulse . . . 58
4.16 Software Algorithm . . . 61
4.17 Pulse time measurement . . . 62
4.18 Data and Serial Message With CRC . . . 63
4.19 Prototype Hardware Design . . . 64
4.20 SENT Transceiver Simulator . . . 66
5.1 A typical IBIS file . . . 68
5.2 An electrical equivalent model of an output buffer . . . 68
5.3 Model Description . . . 69
5.4 The Spartan-3 FPGA-Flash Memory interface and simulation setup 70 5.5 Representation of 12-bits data in the form of SENT-Encoding . . . 72
5.6 Transmission line effects on rise-fall times of the SENT-Signal . . . 73
5.7 Representation of 12-bits data in the form of PWM-Encoding . . . 73
5.8 Transmission line effect on Rise-Time of PWM pulse . . . 74
5.9 Transmission line effect on Fall-Time of PWM pulse . . . 75
5.10 Frequency is 1KHz and data bits are 10 bits . . . 75
5.11 Frequency is 1KHz and data bits are 100 bits . . . 76
5.12 Frequency is 10KHz and data bits are 100 bits . . . 76
5.13 Frequency is 50KHz and data bits are 10 bits . . . 77
5.14 Frequency is 1MHz and data bits are 10 bits . . . 77
5.15 Frequency is 10MHz and data bits are 10 bits . . . 78
5.16 Frequency is 50MHz and data bits are 20 bits . . . 78
5.17 Frequency is 100MHz and data bits are 20 bits . . . 79
5.18 Frequency is 150MHz and data bits are 50 bits . . . 79
5.19 Frequency is 200MHz and data bits are 50 bits . . . 79
5.20 Frequency is 250MHz and data bits are 10 bits . . . 80
5.21 Frequency is 1KHz and data bits are 100 bits . . . 80
5.22 Frequency is 100KHz and data bits are 100 bits . . . 81
5.23 Frequency is 50MHz and data bits are 100 bits . . . 81
5.24 Frequency is 150MHz and data bits are 100 bits . . . 81
5.25 Frequency is 250MHz and data bits are 100 bits . . . 82
6.1 Execution power comparison of fixed-point and floating-point designs 89 6.2 Resource utilization of Fixed-point and Floating-point Designs . . 90
6.3 Memory Footprint Comparison of all the Design Prototypes . . . . 91
6.4 Experimental Setup Nios based design . . . 92
6.5 Experimental Setup PIC based design . . . 93
B.1 SENT Transceiver Simulator . . . 105
4.3 Fixed point algorithm . . . 59 5.1 SENT data-signal start and stop timing . . . 73 6.1 Execution Power Comparison of Floating Fixed Point Implementation 87 6.2 CPU Utilization of Fixed-Point and Floating-Point Designs . . . . 88 6.3 Resource utilization of Fixed-point and Floating-point Designs . . 89 6.4 CPU Utilization of an 8-Bit Platform . . . 90 6.5 Resource utilization of 8-bit Platform Prototype . . . 91
List of Figures xi
List of Tables xiii
Contents xv
1 Introduction 1
1.1 Background . . . 1
1.2 Automotive protocols challenges: . . . 2
1.3 Thesis Objectives and Tasks . . . 3
1.4 Delimitation . . . 4
1.5 Thesis Structure . . . 4
2 Theoretical Background 7 2.1 Communication Protocols in Automotive . . . 7
2.1.1 Communication Requirements for Automotive System . . . 7
2.1.2 Local Interconnect Network . . . 8
2.1.3 Pulse Width Modulation . . . 11
2.1.4 Controller Area Network . . . 13
2.1.5 Single Edge Nibble Transmission Protocol . . . 15
2.2 Hardware Platforms . . . 21
2.2.1 Nios II Processor . . . 21
2.2.2 DE2 Board . . . 23
2.2.3 Microchip-PIC Microcontroller . . . 24
2.3 IBIS Model . . . 26
2.4 ADS-Advanced Design System Tool . . . 27
2.5 Sensors in automotive . . . 28
2.5.1 Position or Speed sensor . . . 29
2.5.2 Temperature Sensor . . . 30
2.5.3 Linear Hall Sensors TLE4998X . . . 32
2.5.4 Mass air flow sensors - MAF . . . 33
2.5.5 Tire pressure sensors or TPMS . . . 33
2.5.6 Throttle Position sensors - TPS . . . 33
2.5.7 Manifold air pressure sensor - MAP . . . 33
2.5.8 Fuel pressure sensor - FPS . . . 33 xiii
2.5.9 Crash sensors . . . 33
2.5.10 Airbag side impact sensor . . . 34
2.5.11 Exhaust gas Sensors . . . 34
3 Comparison of Automotive Communication Protocols 35 3.1 Overview . . . 35
3.2 Comparison of Network Protocols . . . 36
3.3 Features Comparison of Network and Point to Point Protocols . . 38
4 SENT-Protocol Implementation on two different platforms 41 4.1 Research Method . . . 41
4.2 Decisions and method . . . 43
4.2.1 Hardware Platforms . . . 43
4.2.2 SENT-Decoder design on Altera FPGA DE2 Board . . . . 43
4.2.3 SENT-Decoder design using Microchip PIC18 . . . 44
4.2.4 SENT-Transmitter (Sensor) Module . . . 45
4.3 SENT data frame Transmission and Reception . . . 47
4.3.1 SENT data frame Structure . . . 47
4.3.2 Data Message Encoding . . . 48
4.3.3 Data-Message Decoding . . . 48
4.3.4 CRC Calculation . . . 50
4.3.5 Short serial message . . . 51
4.4 Nios-II Based Prototype . . . 51
4.4.1 Development Environment Setup . . . 51
4.4.2 Integration of Hardware and Software . . . 53
4.4.3 System design in SOPC builder . . . 53
4.4.4 Software Design . . . 55
4.4.5 Design with Floating-point . . . 56
4.4.6 Design with Fixed-point . . . 57
4.4.7 Software Algorithm . . . 60
4.4.8 Code profiling . . . 62
4.5 Prototyping with PIC-Microcontroller . . . 63
4.5.1 Hardware setup . . . 63
4.5.2 Software Design . . . 64
5 Signal Integrity Analysis of SENT and PWM with Simulation 67 5.1 Design Overview and IBIS Models . . . 67
5.2 Simulation Overview . . . 69
5.3 Signal integrity analysis of SENT and PWM signals . . . 71
5.4 SENT and PWM signal simulations at frequency range ( 1KHz-250MHz) with different data rate (10-Bits-100-Bits) . . . 75
6.3 Design prototypes comparison implemented with fixed-point and
floating-point . . . 87
6.4 Design prototypes comparison implemented on an 8-bit and a 32-bit platforms . . . 89
6.5 Functional testing of the Nios Based design prototype . . . 92
6.6 Functional testing of the PIC Based design prototype . . . 93
7 Conclusions and Future Work 95 7.1 Summary of Contribution . . . 95
7.1.1 Design with fixed-point and floating-point arithmetic . . . . 95
7.1.2 Prototype design on 8-bit and 32-bit platforms . . . 96
7.1.3 SPICE-Simulation Model . . . 96
7.2 Limitation and Future Work . . . 96
7.2.1 SENT-signal EMC emissions analysis . . . 96
7.2.2 Performance comparison of software-design with the IP-core 96 7.2.3 Sensor fusion prototype with SENT-Interface . . . 96
7.2.4 ON-Chip Interconnect Communication . . . 97
Bibliography 99
A SENT-Decoder CRC Implementation 103
This thesis focuses on the implementation and signal analysis of the Single Edge Nibble Transmission protocol (SENT) described by SAE J2716 SENT [46]. SENT is a point-to-point digital protocol used to interface high resolution sensors to Electronic Control Unit (ECU) in modern automotive systems. In this chapter we will focus on some features of SENT protocol and their applications in automotive systems. The complete introduction of SENT protocol and its comparison with the conventional PWM (Pulse Width Modulation) also with some other point to point digital protocols will be described in details in up coming chapters. This chapter also includes thesis objectives and layout of thesis report.
1.1
Background
Today modern vehicles are equipped with a large number of smart sensor modules which are capable of accurate sensing, signal conditioning and produced digital output that can be interface with microcontroller without any prior conversion (ADC or DAC). In order to retrieve the high resolution information remotely from these sensors the signal integrity and robustness should be ensured. Up to the recent times the conventional Pulse Width Modulation (PWM) was the most commonly use interface between sensors and ECU in automotive systems [5]. But the high resolution output form sensors, real time, safety critical, electromagnetic compatibility (EMC) requirements and low cost overhead demands for more robust and standardized interface. To accommodate the previously mentioned require-ments the Society of Automotive Engineer (SAE) has developed a low cost digital point-to-point interface for unidirectional sensor data the interface is called Single Edge Nibble Transmission (SENT) protocol [46].
SENT protocol was initially adopted for the powertrain [6] applications in automo-tive but because of its low implementation cost and maintaining greater integrity of high resolution sensor data, also due to its more robustness to noise make it more appealing for other automotive and non-automotive applications. The situation
where data transmission from a sensor module to an ECU is required, interface using bus communication protocols such as Controller Area Networks (CAN) [37] and Local Interconnect Network (LIN) [38] are not suitable due to their high im-plementation costs. In such situation SENT protocol is a better replacement for CAN and LIN. As mentioned earlier SENT protocol overcome some of the defi-ciency of PWM. For example the resolution of PWM greatly degrades with the higher clock frequency F c and also PWM provides limited information regarding diagnoses and status of data message. Due to the steep edges from high to low or low high transition of a PWM pulse make it more prone to noise while in the SENT pule rise and fall time are longer compare to PWM which makes it less immune to noise. A complete SENT frame allows transmission of multiple data messages.
1.2
Automotive protocols challenges:
Efficiency of modern cars is measured in terms of safety, fuel efficient and low cost. Electronics modules are included at high speed in automotive systems with the evolution of automotive system design [36]. A number of ECUs are used in today’s car these ECUs communicate to each other and also to off-ECU sensor modules by using communication standards and channels. In recent years a numbers of communication protocols have been proposed to reduce the communication cost between ECUs and sensing units. Safe and high resolution data transmissions are the two main challenges for developing automotive communication standards for communication between sensors and ECUs. Twisted pair cables are commonly used for communication between ECU and sensor module as depicted in the figure 1.1.
Figure 1.1: SENT senor and receiver communication interface
Due to the long distance between the ECUs and off-sensor modules the wire length plays a vital rule in the distortion of signal-(data). A pair of parallel wires acts like a transmission line when high frequency, short period pulses are applied to the channel for high resolution data transmission. The channel line behaves a series of inductance and capacitance which can be model as a lumped circuit an element of wire segment is shown in figure 1.1. A number of techniques are used to achieve high data rate with less signal loss for designing automotive communication standards such as PWM technique. There is a trade-off to achieve high resolution
1.3
Thesis Objectives and Tasks
As previously stated performance and signal integrity are the important factors to be considered while developing new communication standards for an automotive system. Due to the advancement more electronic are included in to automotive system to increase the safety and performance while doing this a huge number of wires are used for communications among ECUs and sensors units. Due to this the wiring cost become significant high and also the transmission line effects produces a number of bit error in the signal which destroy the integrity of data. The motivation for developing Single Edge Nibble Transmission (SENT) protocol was to overcome these issues.
This thesis work focuses on the development of SENT protocol decoder and its signal robustness analysis in comparison with the conventional PWM signal.The first goal of this thesis work is to perform a comparative study of different automo-tive communication protocols in order to understand the challenges that demand for new communication standards. The comparison will be based on their fea-tures and feasibility for specific applications. The second goal is to developed SENT-Protocol in software on the available microcontrollers to check how much memory foot print is used and how much the processor overhead. To achieve the purpose of this goal two platforms has been used. The software implementation is done with two different design algorithms fixed-point and floating-point. The 32 bit platform (Nios-II soft-core processor) has been used, which is provided by Altera FPGA DE2 board for SENT decoder. To check for a low cost and high performance solution, SENT-decoder are developed with 8-bit platform and are compared with the two previous designs prototype to check how much memory foot print is used and how much is the processor overhead. The last goal is to an-alyze the signal integrity for PWM and SENT signal using spice simulation. This can be achieved by developing the complete transceiver and channel SPICE model in SPICE simulation tool. The purpose is to check the maximum data rate limit that the PWM signal support with out creating any bit error in the transmitted signal. The same data rate is then used for SENT signal to be compared with PWM signal.
In order to achieve these goals first a details study has been performed on dif-ferent point-to-point and network based protocols. The SENT-decoder prototype is designed by first performing a details study of SENT protocol to specify the requirements for implementation. The SENT decoder system has been design in the SOPC builder a utility provided by the Quartus II IDE. The design system is compiled and loaded to DE2 board to program the FPGA chip. To evaluate the performance and resource usage analysis of SENT decoder two applications are developed in NIOS II IDE (Integrated Development Environment) using C-Programming language with fixed-point and floating point algorithms. The
de-sign prototype is tested by connecting the SENT sensor module to DE2 board and receiving the data messages from the sensor module in NIOS II IDE console. Secondly to check for the alternative low cost solution another prototype has been developed on 8-bit platform using PIC18 microcontroller together with MP-LAB IDE which is provided by Microchip. The performance and resource usage of both prototypes are also compared to check for a good design prototype. To analyse the signal distortion over the channel for PWM and SENT. The SPICE simulation model has been designed in the ADS-2008 (Advanced System Design) tool from Agilent technology which is a very powerful tool for signal integrity analysis. The channel is model as lumped circuit elements and IBIS model are used for both input and output buffers models. To analyse the effect of the transmission line on both SENT and PWM signals different frequencies range and data rate are set for performing simulation.
1.4
Delimitation
In this thesis our focus is mainly on implementation of SENT protocol on two different platforms to evaluate the performance and robustness of the SENT signal. For verification and analysis of our implementation we will not use any off-the-shelf sensor with the SENT-decoder module instead we will use a custom developed SENT-transmitter (sensor) module which is described in chapter 2 section 4.2.4 for evaluation of the design SENT-decoder prototypes. In this thesis work the analysis of SENT protocol is mainly based on prospective of its use in automotive systems and no other application areas.
1.5
Thesis Structure
This chapter describes the motivation for this thesis work and also provides the layout and delimitation of our work.
In Chapter 2 a detailed study of most commonly used automotive communica-tion are performed.SENT protocol and specially the frame structure of SENT has been described in detailed to specify the requirements for implementation. The development platforms for SENT decoder implementation are also described in this chapter.Some sensors that are most commonly used in automotive system are described at the end of this chapter.
In chapter 3 a comparative study has been performed on the most common point-to-point protocols with SENT protocol which are used nowadays in the automotive industry. Also the features of network based protocols are described in comparison with the point-to-point protocols.
Chapter 4 describes the details of SENT decoder prototype design. Also it de-scribes how the design decisions are made to implement the SENT decoder in software. The two different software algorithm are explain in details. The IDEs
chapter. In Chapter 5 also a complete description are given about the SPICE-simulation model of the SENT receiver module, transmitter module and the chan-nel SPICE model. Each module of the SPICE simulation design is describe in this chapter. Finally in this chapter the complete simulation design are presented. The results are presented in chapter 6. The performance analysis of the design prototypes are presented in this chapter. This chapter also describes evolution of the resource usage of the design prototypes. Simulation results for signal integrity analysis are evaluated for both SENT and PWM in this chapter.
Chapter 7 describes the contribution of our work and gave some ideas for further research in this area. The appendixes consists some schematics and tables which has been used in this thesis work.
This chapter will described the background for this thesis. We will describe some of the important protocols standards that are used nowadays in the automotive system. These protocols standards are either serial (point-to-point) or network based. The structure and applications of these protocols will be describe in this chapter and their comparison will be presented in the next chapter. This chapter will also describe the platforms that are used for the implementation of the design prototypes. The description of Altera DE2 board and SOPC builder together with the Nios II soft-core processor are given in this chapter. PIC18F67J50 development board for 8-bit processor based prototype is also describe in this chapter. Some of the the most commonly used sensors in the automotive system are describe. ADS (Advanced Design System) SPICE simulator from Agilient technology which is used for signal integrity analysis is also describe in this chapter.
2.1
Communication Protocols in Automotive
In this section we will present different bus and point-to-point protocols to interface sensors modules to ECUs in the automotive systems.
2.1.1
Communication Requirements for Automotive System
The selection of a communication protocol in a vehicle depends on types of com-ponents. For example for adaptive damping system [7] FlexRay [8] is a suitable protocol due to its high data rates . The general requirements for in-vehicle com-munication protocols are described as:Determinism:
In automotive system some of the system are time critical and their exact response time should be known. For example in safety critical systems a protocol must ful-filled the deterministic behavior of messages between two components in a vehicle which are responsible for safety related functions.
Tolerance:
Its not necessary in vehicles that all systems should have fault tolerant functional-ity but some systems should continue their proper operation even in the presence of faults. A communication protocol in automotive system should be capable of re-liable communication. The examples of the systems which requires highly rere-liable communication are X-by-wire systems.
Bandwidth:
The communication bandwidth in vehicle is application as well as protocol depen-dent. For example a bus protocol which connect several ECUs requires greater bandwidth. Multimedia application require higher data rates and communication channel bandwidth.The requirement for the higher bandwidth in point-to-point protocol is less than bus protocol.
Flexibility:
The performance of a communication protocol should not be degraded with the addition of system or sub-system functionality. Due to the rapid advancements in addition of new features in automotive systems the communication protocol needs to be more flexible and scalable.
Security:
In order to secure the data transmission in automotive systems the data encryption mechanism should be described for communication standards [42]. The security become more important when vehicle system are exposed to out side world such as remote diagnosis and inter vehicle communication.
2.1.2
Local Interconnect Network
Local Interconnected Network OverviewLocal Interconnected Network(LIN) [38] is serial asynchronous bus protocol. To-day, auto-mobiles are extensively equipped with electronics modules for safety, control and luxury. As the complexity and requirements for addition of more features increases the cost of the system increases too. In 1999 LIN Consortium consists of a group of the world leading car manufacturing companies presented LIN to reduce implementation cost for low data rates systems. LIN is based on existing UART protocol. The key features of LIN protocol are:
• LIN is a bidirectional used single wire • 20Kbits/sec transfer rate
• Support for power management
• Single master and multiple slaves architecture exclude the cost for additional synchronization
LIN Application Areas
LIN is a low speed and low cost sub-bus protocol which target application in ve-hicles in non-safety components. Figure 2.1 shows LIN application in automotive. Some of the typical applications of the LIN protocols are [10]:
Figure 2.1: LIN typical applications in automotive • Vehicle roofs (rain sensor,light sensor,light control,sun roofs,etc.)
• Vehicle doors (Mirrors, Central locking, Mirror switch, Window lift, etc.) • Steering wheel(Cruise control, wiper, radio climate control switches, etc.) • Seat (Set position motor, set heater, occupancy sensor)
• Vehicle roofs
LIN Protocol Description
LIN protocol exploit the features of I2C [45] and RS232 [11]. Like I2C bus is pulled high via resistor while open collector driver is used to pull the bus low, instead of using clock line as in I2C the message is transmitted asynchronously byte by byte marked with start and stop bits as in RS232. In LIN nodes are arranged in master and slave relationship. A LIN master can have upto 16 slaves. The information between nodes is exchanged via LIN frames. The master node is responsible for
synchronization and communication initialization with slaves. Figure 2.2 shows the nodes arrangement in a typical LIN network.
Figure 2.2: LIN typical network overview
LIN Frame Structure
A typical LIN frame comprises of header and response. The header part of LIN frame is always generated by the master node while response can be generated by master or slave. As shown Figure 2.4 in the header consist of three fields synch break, synch field and ident field. The synch break has fixed 13 bits length. Synch break is issue by master node to inform the slaves that a message is ready. Synch field set the clock for entire bus. Its value is HEX-55 including start and stop bits plus 1 bit synch delimiter. A 15% clock drift is allowed between master and slaves. The inclusion of this field in LIN frame eliminate the use of crystal for precise clock synchronization. The third part of the LIN header is ident field which specify what type of data will be on the bus which node should respond to it and how long should be response. In ident field is further divided into three fields 4 bits (0-3) are used to address devices, 2 bits (4-5) indicate the message length to follow and the last 2 bits (6-7) are parity bits. A slave can respond when master commands it. the slave response can be 2, 4 or 8 byte long. The slave nodes can transmit and receive data directly to each other without involving master if commanded by the master.
Pulse Width Modulation(PWM) is a way of representing an analog signal levels into digital waveform. To achieve PWM a digital waveform width is varied with respect to a specific instantaneous value of the analog signal. Different chip ven-dors includes PWM modules in their products. In microcontrollers the encoding and decoding of PWM is performed using timers and comparators modules but the hardware can also be produced with simple electronics circuits without any central controller. PWM has a simple point to point connection as shown in Figure 2.51 a sensor module which transmit PWM signal is directly connected to PWM
decoder for information retrieval. The main features of PWM are:
• Ease of implementation
• Better noise immunity
• Highly available hardware
• One wire requirement for data transmission
• Wide applications domain
Figure 2.4: LIN frame structure
1The signal timing diagram and the interface line are represented by a single line for figure
Figure 2.5: Point-to-Point communication with PWM
PWM Application Area
PWM controllers are widely used for DC motors speed control, LED light control and switching mode power supplies due reduce power losses in power switching. In automotive the most obvious uses of PWM are:
• Electronic throttle control • Seats heating
• Back lights LED lamps control PWM Encoding and Decoding
Some characteristics of signal are used to express PWM signal: period is the time for complete cycle of PWM pulse and duty cycle is the percentage of period for which the signal is high. The simplest technique to generate PWM signal is by modulating the sawtooth waveform with analog waveform this scheme is shown in Figure 2.6 and the resultant PWM waveform is shown in Figure 2.7.
Figure 2.7: PWM waveform
2.1.4
Controller Area Network
Controller Area Network Overview
Controller Area Network(CAN) [37] is message based serial bus protocol developed and released by BOSCH in 1986. CAN is a two wire bus protocol, all nodes accesses the bus with same speed. Figure 2.8 shows typical CAN nodes connection diagram. The BOSCH CAN specifications [37] is divided into two parts: Standard CAN and Extended CAN. The major difference between two is the length of identifier. CAN has been standardized by International Standardization Organization (ISO). CAN definitions can be found in ISO 11898 and ISO 11519 standards. CAN applications domain is not limited to automotive only but also has applications in industrial automation and medical equipments. The main features of CAN protocols are:
Figure 2.8: CAN nodes connection diagram
• Real time communication upto 1 Mbits/sec speed
• Supports high saturation of nodes in a single CAN network(theoretically more than 2K nodes)
• Hardware support available from all major chips vendors • supports robust error handling and remote diagnosis • Provides extremely flexible and scalable system integration CAN Application Area
CAN protocol initial design was specific for automotive application but it has been adapted for several industrial automation and real time control in various industrial applications. Figure 2.9 shows the typical CAN applications for both CAN high speed and CAN low speed buses in automotive.
Figure 2.9: CAN bus typical applications in automotive CAN Protocol description
CAN allows multiple master nodes to exist in a single network. It utilizes Carrier Sense Multiple Access/Collision Detection(CSMA/CD) algorithm to check the bus status before sending messages on the network and uses arbitration based on mes-sage identifier. When bus is free any CAN unit can start transmission, if two or more CAN nodes start transmission at same time the node with higher message priority succeed while the node with lower priority back off and wait for random amount of time until the bus become free again. CAN CSMA/CD differ from Ethernet protocol in the respect that if a collision is detected the messages are not completely destroyed but the message with higher priority always succeed. CAN Data Frame Structure
CAN has four types of frames: Data frame, Remote frame, Error frame and Over-load frame but here we will discuss only the data frame. Figure 2.10 and Figure 2.11
Figure 2.10: CAN bus typical applications in automotive
Figure 2.11: CAN extended frame structure
shows the CAN data frames structures for standard frame and extended frame. As described earlier the main difference between the two formats is the length of identifier field. The first field of the CAN message is Start Of Frame(SOF) is 1 bit long, indicate the beginning of the message. SOF field is followed by Arbi-tration field which comprises of 11 bits or 29 bits message identifier depends on whether the frame is of standard or extended version and 1 bit Remote Transmis-sion Request(RTR)fields which is used to request data from another CAN node. In extended frame format arbitration field includes two extra 1 bit long fields: Substi-tute Remote Request(SRR) used for arbitration between standard and extended frames and Identifier Extension(IDE) which differentiate the two formats. Arbi-tration field is followed by 6 bits control field which consists of two parts Reserved bits(r0, r1) 2 bits in length and 4 bits Data Length Code(DLC) which specify the numbers of bytes in the data field that will follow. Data field is 0 to 64 bits. A 15 bits Cyclic Redundancy Check(CRC) field and 1 bit CRC delimiter(DEL). CRC field is followed by acknowledge(ACK) field which includes 1 bit ACK slot and delimiter DEL. The last field in a CAN frame is End Of Frame(EOF) consisting of 7 bits to indicate the end of message.
2.1.5
Single Edge Nibble Transmission Protocol
Single Edge Nibble Transmission(SENT) is a new digital point to point commu-nication protocol. It is a unidirectional commucommu-nication between sensors and the ECU. There is no coordination signal from the receiver (ECU). SENT frame con-sist a series of pulses in which the data can be measured between two falling edges times. It was first introduced by the power train division of General Mo-tors and several other partner companies in 2005. SENT was first developed by a workgroup of Society of Automotive Engineers(SAE) later on it became an in-ternational standard SAE J2716 [46]. It is promising low cost alternative to the CAN and LIN standards. SENT can be used in those application where high res-olution data needs to be transmitted from sensors to ECU. Multiple derivative of SENT protocol are developed like Short PWM Code(SPC) [40] which is similar to the SENT basic standard proposed by SAE but SPC provides a synchronization
mechanism and shorter transmission time due to the utilization of the number of nibbles for encoding data. The developed SENT/SPC driver has the support for all Infineon Technologies programmable linear Hall sensors such as TLE4998C [12] it is also compatible with TLE4998C supported SPC modes and SENT/SPC frame formats. Another SENT decoder implementation is provide by Infineon technologies called SENT decoder for XC2000 [47] which is a complete software package. The receiver has the support for the following features:
• Reception and decoding of SENT frames • Configurable number of data nibbles per frame
• Configurable SAE SENT or Infineon specific SENT protocol receiver • Serial data decoding Error detection
The INTRINSIX technology developed a SENT Silicon IP transmitter module [13] which is fully compatible with SAE international J2716 communication standard. This IP is flexible and the data nibbles can be configure for different sensors according to the required application. The IP has also interfaces for AMBA and APB. The developed IP is based on Verilog RTL design that can be used for any FPGA technology. It can be consider an alternate to lower resolution 10-bit A/Ds and PWM. The design of SENT silicon IP module is depicted in the given Figure 2.12 a detailed explanation will be presented in section 4.5.
Figure 2.12: RTL design of SENT IP [14]
Melexis (Microelectronic Integrated Systems) developed MLX90324 [15] which is a monolithic sensor IC and only sensitive to the flux density coplanar with the IC
The output is selectable between Analog, PWM and SENT (SAE-J2716) Proto-col. The functional block diagram of MLX90324 is depicted in Figure 2.13 [15]. According to the functional description shown in Figure 2.13 it is clear that the output can be selected among three different formats. The details explanation about MLX90324 will be presented in section 4.5.
Figure 2.13: MLX90324 functional block diagram SENT Application Areas
SENT protocol is an alternative to conventional CAN and LIN communication standards. So the targeted area of applications is all most same as CAN and LIN but it is rather simple to implement and has the possibility of high data rate. Some of the typical applications of SENT protocol are given below.
• Vehicle steering system for measuring steering angle or steering torque. • Automotive chassis
• Rotary Position sensors and pressure sensors • Throttle Position Sensors
• Mass air flow sensors
• Can be use as an alternative to lower resolution 10-bit A/Ds and PWM • Temperature sensors
SENT Protocol description
The SENT frame is defined by a series of pulses in which the data are measured between the two falling edge times. The first pulse is synchronization or calibration pulse which is followed by Status or communication pulse. After the synchroniza-tion pulse all the 8 pulses are 4 bit (one nibble) long and there are eight nibbles
after the synchronization pulse is depicted in Figure 2.14. The pause pulse is op-tional and it is defined in the new SAE J2716, JAN2010 standard. There are six data nibbles the nibble value can be varied between (0-15). CRC nibble is use for signal integrity purpose. Figure 2.14 describe the basic telegram of the SENT protocol. The following are some features of the SENT protocol.
Figure 2.14: SENT frame
• It is a unidirectional (one wire) point to point protocol
• The data transmission is independent of the receiver no calibration from the MCU
• Simple Electromagnetic Compatibility(EMC) filter for the detection of SENT signal
• 20% clock variation is allowed for transmitter
• Due to the large rise and fall time of the pulse, SENT signal is more robust to noise
SENT Data Frame Structure
The transmitted SENT frame from the sensor module is represented by a sequence of pulses. The complete message contains two 12 bits sensors information the whole frame is divided into 8 nibbles after the synchronization pulse. The length of Synchronization pulse is 56 clock ticks if there is no variation in the transmitter clock frequency. SAE J2716 standard described a 20% variation in the transmitter clock frequency according to this feature of SENT specification the synchronization pulse time can be varied between (48.8 - 67.2) clock ticks. The basic unit of time is called a clock tick and its value can be in the range (3usec to 10usec) according to SAJ J2716 specification. Figure 2.15 describe the SENT frame format the second pulse after the synchronization is called status or communication pulse which is 4 bits (one nibble) wide.The length of each nibble can be calculated as (12 + N) where N is the nibble values which can be varied between (0 -15).
Figure 2.15: SENT frame structure
The nibble value depends on the amount of data being encoded in the data nibble. The 24 bits data are represented into two signals each 12 bits long. To understand the complete SENT transmission sequence each pulse can be individually explain as follows:
Synchronization or Calibration pulse: The synchronization pulse is 56 clock ticks long. The receiver can resynchronize with the sensor module by measuring the exact time unit from the synchronization pulse of the transmitted signal. The total length of the pulse is 56 CTs the first five CTs are low and the reaming is high is shown in Figure 2.16. The actual sensor data is measured during the synchronization pulse.
Figure 2.16: SENT synchronization pulse
Status or Communication pulse: The status nibble is use for diagnostic pur-pose. The first two bits are reserved for specific applications like part number and error information. The 3 and 4 bit of the status nibble can be used to send a short or enhanced serial message specified by SAE J2716. One bit of a serial message can be send during each SENT complete frame transmission to send a 16 bit serial message 16 consecutive transmissions are needed.
Data Pulse: The data nibble pulse is used to transmit the actual of the sensors module to the ECU. A maximum of six data nibbles (24 Bits data) can be transmit in one complete frame. The 24 bits data are divided into two signals each carries three data nibbles is depicted in figure 4. The width of the data nibble pulse varied with the nibble value and can be calculated according to the formula. Data nibble pulse width = (12 + Nibble Value) where the nibble value change from 0 to 15. CRC Pulse: For the data integrity the SAE J2716 Specification provide a 4 bit CRC checksum nibble. The CRC checksum is calculated using the polynomial x4+ x3+ x2+ 1 with the seed value 5 (0101). The checksum is only calculated for
data nibbles and not for status nibble. The following error can be detected with this crc checksum:
• All single bit errors. • All odd number of errors.
• All single burst errors of length â 4 • 87.5% of single burst errors of length = 5 • 93.75% of single burst errors of length > 5
clock ticks.
2.2
Hardware Platforms
To achieve the goals of the thesis which are described in the first chapter. The selection of hardware platforms is made on the bases of the thesis requirements. In this section we will introduce the hardware platforms and their respective tools that are used for the prototyping and implementing of SENT protocol to achieve the goals of this thesis work. The SENT has been implemented on two different hardware-platforms: Altera Nios II and Microchip PIC microcontroller for the analysis of cost, resource utilization and performance. In the coming sections we will present each of these platforms and their accessories for development of SENT protocol. The complete details of their implementation will be described in the next chapter.
2.2.1
Nios II Processor
Nios II is 32-bits Reduce Instruction Set Computer (RISC) soft core architecture developed by Altera for their FPGA families. Because of its soft core Nios II is very configurable and flexible. It provides customization options to its developer that can be selected on the bases of system design requirements. The Nios II processor core block diagram is shown in Figure 2.17.
The general features offered by Nios II cores are:
• 32-bit instruction set, data path and address space
• 32 general purpose registers with optional shadows registers
• Floating point instructions for single precision floating point operations • up to sex-stage pipeline depth(differ within cores)
• Single instruction multiply and barrel shifter • Access to 2 GB of external address space • Branch prediction
• Optional memory management unit (MMU)and Optional memory protection unit(MPU)
• Hardware-assisted debug module enabling processor start, stop, step, and trace under control of the Nios II software development tools
Nios II processor has three different types of cores: Nios II/f (Fast), Nios II/s (Standard) and Nios II/e (Economy). These cores are shown in the Figure 2.18, which is taken from the SOPC builder in quartus II design tool. The processor that we use for the implementation of our design is Nios II/e (economy) type which is highlighted in yellow in the Figure 2.18. The difference among these cores in term of performance, area, and memory utilization is given in the Figure 2.18.
the both cores standard and economy type.
Nios II/s (Standard): Nios II/s "standard" processor core implements a small processor core without a significant trade-off in software performance. The ALU of standard and fast cores provides the same performance. The standard core has the five instruction pipeline.
Nios II/e (Economy): The core size is smaller than standard and fast type. There is no instruction pipe line in this core only fetches one instruction at the time. It is good for those applications where the implementation cost is required to be less.
2.2.2
DE2 Board
Altera DE2 is a development and educational board which is based on Cyclone II Field Programmable Gate Array (FPGA) chip. DE2 board [16] is a complete embedded system and provides the ideal vehicle for learning and quick prototyping of design project in industries and academic sectors. The DE2 board provides a variety of features for the implementation of huge number of design projects also use for development of digital systems. The block diagram of the DE2 board is shown in the Figure 2.19
All these devices which the DE2 board provides are connected through the cyclone II FPGA so the user can configure the FPGA according to the requirement for their system design. DE2 board is provided with the quartus II hardware design tool and Nios II embedded processor a software design tool. The three tools DE2 board, Nios II and Quartus II provides complete platform for the hardware and software co-design of any system design. There is a large amount of learning material for students and researchers are available on Altera website and also with the de2 board accessories. For the design and prototyping of our system design we use the DE2 board along with Quartus II software and Nios II processor IDE. The complete description of our implementation and how we used these tools will be presented in the next chapter. Some of the devices that we used in our system design are highlighted in yellow in Figure 2.19.
2.2.3
Microchip-PIC Microcontroller
We used PIC-microcontroller as an 8-bit processor for the implementation to be compare with the Nios II 32-bit processor. This section provides a short intro-duction to the PIC-microcontroller and the details description will be given in the implementation part. Microchip Technology Corporation introduced an 8-bit microcontroller in 1989 called PIC (Peripheral Interface Controller). Later on they introduced an array of 8-bit processors. The PIC microcontroller families in-clude PIC10XXX, PIC12XXX, PIC14XXX, PIC16XXX and PIC18XXX. Besides this Microchip now also produces 16-bit and 32-bit microcontroller they called (PIC24-16) bit and (PIC32-32 bit) series respectively.
designs because of its availability in different pins packages from 18 pins package to 80 pins package also it is inexpensive and all the required hardware is available on the one chip. We select the PIC18F67J50 member PIC18 family for the design of our system due to its low power consumption and USB boot loader which is really easy to reprogram the device. The PIC18F67J50 is available in the form of small development board as shown in Figure 2.20 on the previous page from the Robot-Electronics UK [1]. The details description about the implementation of this board will be presented in the implementation part.
PIC18F67J50 Microcontroller
PIC18F67J50 has RISC (Reduced Instruction Set Computer) architecture. This is the member of a new PIC18 family called PIC18F87J50 USB microcontrollers. This family has an advantage over the traditional PIC18-microcontrollers because of its high computational power, low-voltage USB and low-price. These features make PIC18F87J50 family an ideal choice for low-cost applications. The devices in PIC18F87J50 family come in two different pin packages 64-pins and 80-pins Figure 2.21 show the 64 pins package of PIC18F67J50 microcontroller.
As shown in the Figure 2.21 there are multiple ports available with some of the ports pins are multiplexed with an alternate function from the peripheral features on the device. Some of the key features of PIC18F87J50 USB microcontroller are • USB (Universal Serial Bus) V2.0 with low speed 1.5Mb/s and High speed
12Mb/s
• Flexible oscillator structure: two external clock modes up to 48MHz. • Peripheral Features:
– Four programmable external interrupts – Two capture/compare/PWM (CCP) modules – Three capture/compare/PWM(ECCP) modules – I2C master and slave modes
– Dual analog comparators with input multiplexing
– Two enhanced USART modules (RS-485,RS-232 and LIN 1.2) supports • External memory up to 2MB addressable
• Low power high speed CMOS technology • Run, idle and sleep modes saving power
There are a number of features which make PIC18F87J50-microcontroller family unique. Some of the family members of this family with the supports they provide are describe in the following table we use PIC18F67J50-microcontroller as a part of our system design which is highlighted in Figure 2.22.
Figure 2.22: PIC18F87J50-Microcontroller Family Member [2]
2.3
IBIS Model
The simulation of digital I/O buffers with its chip packages and PCB can be done using traditional transistor level model approach. To use this approach the ven-dors should provide the complete spice model about their devices which reveals the proprietary device information to solve this problem, behavioral models of devices
as transmission line effect, crosstalk and ringing phenomenon on PCB (Printed Circuit Board). The I/O buffer information is given in the form of voltage-current (VI) and voltage-time (VT) tables together with a set of rise and fall times of the drive output voltage and packages parasitic in an IBIS model. The IBIS model of a digital (I/O) buffer is show in the Figure 2.23.
Figure 2.23: A typical output buffer equivalent circuit
The V/I characteristics of upper and lower device as depicted in figure are given in an IBIS model in two different tables each table consists of max and min values of VI characteristics. The actual VI curve varies between these two set of VI characteristics.
2.4
ADS-Advanced Design System Tool
Adanced Design System is an electronic design automation software for RF, mi-crowave, and high speed digital applications. ADS software is introduced by Keysight EEsof EDA [17]. ADS provides easy to use interface, with a vast verities of simulation modes and models. The most common used is for circuit simula-tion, DC analysis, transient analysis, AC analysis, and S-paramets analysis. The complete tutorial how to make project in ADS can be found here [18].
Applications
• MMIC Design: A Monolithic Microwave Integrated Circuit, or MMIC is a type of integrated circuit (IC) device that operates at microwave frequencies (300 MHz to 300 GHz)
• RFIC Designers
• RF Microwave Board Designers
• RF System-in-Package RF Module Designers • Power Electronics Designers
Key Features
• Complete schematic capture and layout design in the same environment • Circuit and system simulators
• RFIC Designers
• Vast Varities of wirless libraries • Simulation of IBIS Models
2.5
Sensors in automotive
The luxury of today’s modern automotive would not be possible without the use of smart sensors. In order to enhanced the driving experience and provided more safety the modern automotive is equipped with a huge number of smart sensors. These sensors can be used in different part of the automotive systems as shown in figure 2.24
to the work of this thesis. • Rotational motion sensors • Temperature Sensors • Positional/Speed Sensors • Mass air flow sensors • Throttle Position sensors • Linear Hall Sensors TLE4998X • Manifold air pressure sensor • Fuel pressure sensor
• Crash sensors
• Airbag side impact sensor • Exhaust gas Sensors • Tire pressure sensors
2.5.1
Position or Speed sensor
There are different applications of the position sensor in automotive system. The most commonly used is for determining the speed of the vehicle. The position sen-sor can be design using Hall-effect, photo electric effect, and inductive (variable reluctance/pick up coil) principles. The variable reluctance (pick up coil type) is a conventional way of measuring position of the gear tooth. The new speed de-termining sensors are based on the Hall-effect principle. We will describe in detail the construction principle of position sensor based on inductive type technology (Faradayâs law). This sensor consists of a permanent magnet, soft-core and a coil is depicted in the Figure 2.25.
Advantages
• Manufacturing cost is low
• High level EMC low static internal resistance no extra electronic circuitry need for protection.
• Due to the dynamic measuring there is no dc voltage drift problem. • High temperature range
Disadvantages
• Due to the coil technology the size cannot be reduced.
• The output signal depends on the rpm unsuitable for quasi-static moments • It is really sensitive to air-gap fluctuations.
Applications
These are some application areas in automotive where the position or speed sensor can be used
• The sensor can be used as an engine speed sensor to measure the crank shaft-rpm.
• As a wheel speed sensor • Camshaft sensor • Needle-motion sensor
2.5.2
Temperature Sensor
Various types of temperature sensor are used to measure temperature of different parts of automotive system. The design of all these sensors use for temperature measurement based on the principle of thermistor or Temperature sensitive re-sistor, thermocouple and semiconductor barrier layer or PN-Junction diode. To monitor the engine temperature for the proper amount of fuel injection the ECU must know the correct engine temperature. The engine temperature can be mea-sure with ECT (engine coolant temperature) sensor, intake air temperature sensor (IAT) and Exhaust recirculation gases (ERG) sensor. To understand the working principle these mentioned sensors it is important to first understand the operation of a simple thermistor. Most of the thermistor is NTC (Negative temperature co-efficient) its resistance increases with the decrease in temperature. Figure ?? show the typical circuit diagram of thermistor the MCU can measure the temperature from Vout of the thermistor. R1 and thermistor resistance make a voltage divider the change in thermistor resistance results a varying voltage at the junction.
Figure 2.26: Thermistor Circuit Diagram
The ECT sensor works on the same principle of thermistor. The change in temper-ature produces a change in resistance that causes a voltage change on the junction. The ECU sends a reference voltage to the sensor and received the change in volt-age by a feedback line. ECU determines the temperature of engine using the Vref and the feedback voltage this process is describe in the Figure 2.27.
Figure 2.27: Engine Coolant Sensor
A typical engine coolant sensor can measure temperature from -40 to +130Câ◦ degrees. Applications of temperature sensor beside the engine coolant sensor and
there measuring temperature ranges used in various parts of the automotive system as follows
• Air-temperature sensor: it is installed in an intake air passage for calculating the intake air mass the operating range is (-40 to +120Câ◦).
• Engine-oil temperature sensor: This sensor is use for calculating the service interval operating range is (-40 to +170Câ◦).
• Fuel-temperature sensor: This sensor is use for calculating the precise in-jected fuel quantity operating range is (-40 to +120Câ◦).
• Exhausted gas-temperature sensor: The measuring range is (-40 to +1000Câ◦).
2.5.3
Linear Hall Sensors TLE4998X
The Infineon technologies [19] introduced a product family of programmable linear Hall sensors called TLE4998X these sensors can be used in a verities of applications in automotive and non-automotive systems. The working principle is based on the hall-effect phenomenon. These sensors provide digital output protocol which is based three different standards such is SENT (SAJ2716 Standard), PWM, and short PWM codes (SPC). The family is divided into three different types of sensor due to its output protocol they are given below.
• Programmable PWM output-TLE4998P3 • SENT (SAJ2716 standard)-TLE4998S4 • SPC (Short PWM code)-TLE4998C3
The TLE4998S4 [20] is designed for the detection of position and rotation. The operation of TLE4998S module consists of a sequence of steps which is described in simple block diagram is shown in the following Figure 2.28.
Figure 2.28: TEL4998 Linear Hall Sensor
The change in magnetic flux is detected by the hall-effect cell the output signal from hall-effect cell is then converted from analog to digital in the ADC cell to stabilize magnetic offset low pass filtering is done in the LPF cell and the output signal send to DSP unit for signal processing the final output from the TLE4998S module is a SENT signal based on SAJ2716 standard with the resolution of 16 bit.
The MAF sensors are more suitable than the volumetric flow sensors because the density of the air change with temperature and pressure. The most common use is in the electronic fuel injection engines.
2.5.5
Tire pressure sensors or TPMS
The tire pressure monitoring system TPMS is used to gives the information to the driver by a display that the air in the tire are low.
2.5.6
Throttle Position sensors - TPS
The throttle position of the vehicle is monitored by TPS. The throttle position sensor reports the position of the gas pedal to the ECU. The ECU then determine the amount of air flow to the engine and the amount of fuel to be injected to the engine.
2.5.7
Manifold air pressure sensor - MAP
The manifold air pressure senses the engine load. The MAP senses the intake vacuum and respond accordingly. If the vacuum in the intake manifold is wide, the engine sucks in more air and which intern increase the fuel to air ratio. When the intake vacuum drops the engine sucks less air and thus reduced the fuel con-sumption.
2.5.8
Fuel pressure sensor - FPS
The fuel pressure sensor or also called fuel tank pressure sensor is an electronic device, which is used in automotive to measured the quantity of fuel remains in the fuel tank. The measurements are made by sensing the internal pressure of the tank. This data is then passed to power train module (PCM) which in turn passes the fuel need for the engine to the fuel pump.
2.5.9
Crash sensors
Crash sensors make the decisions about the deployment of the air bag on the bases of data it collects from surroundings. There are different types of crash sensors that are equipped in the vehicle, such as frontal crash sensors which is located in the front of the vehicle, near the engine, in the passenger compartment or in the ECU, other examples of crash sensors are side impact sensor and rollover crash sensors.
2.5.10
Airbag side impact sensor
Airbag side impact crash sensors is located in the doors of the vehicle. The sensors are activated when the vehicle is hit on either right or left of the vehicle. They are most commonly installed in the front doors.
2.5.11
Exhaust gas Sensors
The primary purpose of exhaust gas or exhaust gas temperature sensors is to sup-port catalytic converters. But these sensors are also very imsup-portant for protecting components from overheating which are located in the flow of hot exhaust gas.
Comparison of Automotive
Communication Protocols
This chapter presents the comparative study of some of the communication pro-tocols that were introduced in previous chapter. In the previous chapter the main focus was on the protocol description and their features and applications in general while in this chapter we will try to dig a little deeper to explore the challenges that demands for a new communications protocols and their features comparison that makes them feasible for certain applications.
3.1
Overview
Today’s modern cars are the wonderful combination of electronics and mechan-ics. As computer systems are becoming more pervasive, they are also becoming integral parts of objects all around us and cars are no exceptions. The vehicles manufactures are competing for market edge and satisfy their costumers needs by inserting more and more new sophisticated features and gadgets with lower cost. They also have to fulfill regulation requirements related to safety, emission, environment, etc. All these factors somehow contribute in more semiconductor consumption in vehicles. The insertion of semiconductor eliminate some of the bulky and complex mechanical and hydraulic system that results in reduction of over-all system cost, weight and better performance. The inclusion of smart elec-tronics control units makes modern vehicles a complex distributed system with the capabilities of better control, monitoring, scalability, ease of configuration, safety and communication. The intercommunication among these ECUs requires robust and highly efficient communication interfaces with the ability to satisfy the strict timing requirements from different subsystems.
Couple of decades ago in vehicles communication among ECUs was mostly done through point to point interfaces. The side effects of dedicated point to point interface was the size of wiring harness that ultimately results in increase in cost,
weight and difficulties in maintenance. To overcome this problem the network protocols were introduced that effectively reduced the amount cabling harness, brought a lot more flexibility. Embedded systems in vehicles are classified accord-ing to their functionality, architecture and constraints into different domains: pow-ertrain domain, chassis domain, body domain, telematic domain and the passive safety domain. The unique communication requirements of each domain enables the coexistence of multiple protocols in vehicles. SAE classified the in vehicle net-work protocols based on their data rates and functionality. As Figure 3.1 shows the different electronics modules classified according to SAE classifications. The details of the SAE network protocols classes will be presented in the next session. There are a number of protocol standard available for in-vehicle communication.
Figure 3.1: Automotive electronics systems classifications with respect to SAE classes [3]
The existence of standards facilitate the integration of components from suppli-ers that have expertise in the specific product. The industrialization of in-vehicle communication significantly improves the quality of the product and reduces the cost of the system.
3.2
Comparison of Network Protocols
In the previous section we shortly described SAE classification of network pro-tocols. Figure 3.2 shows the most commonly adopted protocols for automotive according to their data rates. As it can be seen in the diagram that a protocol falls in a specific class based on its data rates. It is also clear from the diagram that the protocols with higher data rates have relatively higher communication
Figure 3.2: Automotive protocols comparison based on their data rates [3]
SAE classify in-vehicle protocols into four classes: Class A, Class B, Class C and Class D. Specific protocol standards exist for each class except Class D. Any protocol with data rates higher than 1Mb/s comes under Class D.
Class A: The protocols with data rates lower than 10kb/s comes under the Class A category. As in Figure 3.1 have been shown the automotive electronic modules associated with the body domain are mostly implemented with low data rates protocols. Low implementation cost is the most attractive feature of Class A protocols. But there is lack of globally accepted Class A standard. There are several Class A protocols but the widely adapted are LIN and Time Triggered Protocol (TTP)/A [48]. CAN can also be implemented as Class A protocol. Class B: Class B protocols have data rates between 10kb/s to 125kb/s. The major uses of Class B protocols in vehicles are for general information sharing, di-agnosis, instrumentation and body electronics. J1850 [21] adapted by SAE as Class B standard and has wide acceptance among North American car manufactures.
J1850 has two versions: 10.4kb/s single wire with Variable Plus Modulation(VPM) encoding and 41.6kb/s two wires with PWM encoding. While its counter part and widely accepted among European car manufactures is CAN.
Class C: The data rates ranges from 125kb/s to 1Mb/s. Class C protocols are mainly used for real time control, powertrain control, engine management, etc. A more comprehensive list of Class C protocols applications are shown in Figure 3.1. CAN 2.0 is the most dominate Class C standard protocol. Other Class C protocol standards are SAEJ1939 and SAEJ2284. These protocols adapt CAN as a base so medium access and message formate is consistence with CAN. Another feature of J1939 and J2284 is they target all layers of network model.
Class D: As stated earlier SAE does not specify any standard for the Class D network. Class D protocol targeted area is multimedia applications. The widely adapted protocol for such applications across Europe among car manufactures is Media Oriented System Transport (MOST) [22]. MOST is de-facto standard for multimedia networks in automotive industry. The alternatives to MOST are D2B [43] and IEEE1394 [23].
3.3
Features Comparison of Network and Point
to Point Protocols
Table 3.1 gives features comparison of some of the network and point to point protocols that are widely adapted by the automotive industry. In previous sections we emphasised on the use of network protocols, their advantages and how they contributes in the cost reduction of the system but it will be worth mentioning here. why point to point protocols still exists? Since lowering the cost of system is one of the major factor behind existence of numerous network protocol inside a vehicle, this is also a reason behind the existence of point to point protocols in vehicles. Another reason why point to point protocols still exists is the situation to interface a standalone system. In such situations or the scenarios where only one sided data traffic is required the use of network protocols is waste of bandwidth and resources. These and some other reasons dictate the car manufactures to keep exploring more efficient and cost effective point to point protocol solutions along with network protocols. There are several point to point protocol standards exists that are supported by some of the leading automotive solution provider and actively used by the major automotive vendors. Some of these protocols are SENT, PSI5, PWM, etc.
