CAN Protocol

Introduction

In today’s world, automation is needed in many systems which provide better performance. Large

numbers of systems are fully automated. Vehicle system is composed automotive electrical architectures

consist of a large number of electronic control units (ECU) carrying out a variety of control functions. In

vehicle system we generally want greater safety, more comfort, convenience, pollution control and less

fuel consumption. Modern vehicle may have many electronic control units (ECU) for various subsystems.

Different such subsystems are airbags, antilock braking, engine control, audio systems, windows, doors,

mirror adjustment etc. Some of these subsystems form independent dependent subsystems.

Communications among dependent sub systems is essential.

Traditional electronic control system can improve a vehicle dynamics, economy comfort. But some

problems also have come up, such as the body wiring complexity, space constraints and some reliability

issues. In order to solve these problems, the vehicle network technology has been created. In-vehicle

networking protocols must satisfy requirements which include, significant reduction of wiring harness,

reducing body weight and costs, improving the efficiency of fault diagnosis, low latency times and

configuration flexibility and enhancing the level of intelligent control. Sub-systems (ECU) require the

exchange particular performance and position information within defined communication latency.

Therefore the requirement for each ECU is to communicate via network technology called CAN

(Controller Area Network) bus. The project focuses on using CAN bus protocol for vehicle automation.

Objective:

The goal of this project is to develop few automated features for the driver-vehicle control system using

CAN Protocol. In this project we control switching of the vehicle’s AC/Fan using temperature sensor and

help the vehicle in parking using ultrasonic obstacle sensor. The status of the car temperature and the rear

distance of the vehicle from obstacle are conveyed to the user by displaying on the LCD. The primary aim

of the project is to learn about the CAN Protocol which is a highly reliable protocol and has good real

time performance with very low cost.

Scope of the Project:

The scope of our project is to achieve AC/Engine Heat controlling technique and Vehicle parking system

which can be implemented in all the automobiles. The use of CAN protocol to implement the above

features accurately is our main goal.

With rapidly changing computer and information technology and much of the technology finding way

into vehicles. They are undergoing dramatic changes in their capabilities and how they interact with the

drivers. Hence the automated features inside a vehicle are very much necessary to be achieved. The

AC/Engine Heat control mechanism and vehicle parking system used in our project uses ARM 7

processors and CAN controllers where each ECU is connected across the CAN bus and communicates

with the Monitor ECU. The project can be further extended for vehicle security, cruise control and

electric power steering (EPS), audio systems, power windows, doors, mirror adjustment, battery and

recharging systems for hybrid/electric cars.

BASIC BLOCK DIAGRAM

Basic Block Diagram of CAN communication

CAN is a multi-master broadcast serial bus standard for cis able to send and receive messages, but not

simultaneously.

Each node requires a:

• Central processing unit or host processor

– The host processor decides what received messages mean and which messages it wants to transmit

itself.

– Sensors, actuators and control devices can be connected to the host processor.

• CAN controller; hardware with a synchronous clock

– Receiving: the CAN controller stores received bits serially message is available, which can then be

fetched by the host processor (usually after the CAN controller has triggered an interrupt).

– Sending: the host processor stores it’s transmit messages to a CAN controller, which transmits the bits

serially onto the bus.

• Transceiver

– Receiving: it adapts signal levels from the bus to levels that the CAN controller expects and has

protective circuitry that protects the CAN controller.

– Transmitting: it converts the transmit-bit signal received from the CAN controller into a signal that is

sent onto the bus.

Applications:

The primary applications for this project are for the drivers. The project delivers the following two

features:

ye Blink sensor

2. GPS (Global Positioning System)

Hardware Requirement:

ARM7 – LPC2129:

The ARM architecture is based on Reduced Instruction Set Computer (RISC) principles. The RISC

instruction set and related decode mechanism are much simpler than those of Complex Instruction Set

Computer (CISC) design. This simplicity gives:

A high instruction throughput.

An excellence real-time interrupts response.

A small, cost-effective, processor macro cell.

The ARM7TDMI core is the industry’s most widely used 32-bit embedded RISC Microprocessor

solution. Optimized for cost and power-sensitive application, the ARM7TDMI solution provides low

power consumption, small size, and high performance needed in portable, embedded application. The

ARM7DMI-S is synthesizable version of ARM7TDMI core.

Features:

16/32-bit ARM7TDMI-S microcontroller in a 64 or 144 pin package.

16 kB on-chip Static RAM, 128/256 kB on-chip Flash Program Memory

In-System Programming (ISP) and In-Application Programming (IAP) via on- chip boot-loader

software. Flash programming takes 1 ms per 512 byte line. Single sector or full chip erase takes 400 ms.

Two interconnected CAN interfaces with advanced acceptance filters.

Four channel 10-bit A/D converter with conversion time as low as 2.44 ms.

Two 32-bit timers (with 4 capture and 4 compare channels), PWM unit (6 outputs), Real Time Clock

and Watchdog.

Multiple serial interfaces including two UARTs (16C550), Fast I2C (400 Kbits/s) and two SPIs.

60 MHz maximum CPU clock available from programmable on-chip PhaseLocked Loop.

Vectored Interrupt Controller with configurable priorities and vector addresses.

Up to forty-six, 5 V tolerant general purpose I/O pins.

On-chip crystal oscillator with an operating range of 1 MHz to 30 MHz

Two low power modes Idle and Power-down.

Processor wake-up from Power-down mode via external interrupt.

Individual enable/disable of peripheral functions for power optimization.

Dual power supply.

- CPU operating voltage range of 1.65V to 1.95V (1.8V +/- 8.3%).

- I/O power supply range of 3.0V to 3.6V (3.3V +/- 10%).

Block Diagram of ARM7 – LPC2129:

4.1.1.1 Analog to Digital Converter (ADC):

Basic clocking for the A/D converters is provided by the APB clock. A programmable divider is included

in each converter, to scale this clock to the 4.5 MHz (max) clock needed by the successive approximation

process. A fully accurate conversion requires 11 of these clocks.

Features:

• 10 bit successive approximation analog to digital converter.

• Input multiplexing among 4 pins.

• Power-down mode.

• Measurement ranges 0 V to VREF (typically 3 V; not to exceed VDDA voltage level).

• 10 bit conversion time = 2.44 µs.

• Burst conversion mode for single or multiple inputs

ADC Routine Flowchart:

START

INITIALIZEINPUT PORT- P0.30

START CONVERSION

CONVERSIOIS

DONE?

NO

YES

CONVERTED DATA PRESENT IN ADDR

STOP

Global Positioning System (GPS)

The Global Positioning System (GPS) is a space-based satellite navigation system that provides

location and time information in all weather conditions, anywhere on or near the earth where

there is an unobstructed line of sight to four or more GPS satellites. The system provides critical

capabilities to military, civil, and commercial users around the world. The United States

government created the system, maintains it, and makes it freely accessible to anyone with a

GPS receiver.

The US began the GPS project in 1973 to overcome the limitations of previous navigation

systems, integrating ideas from several predecessors, including a number of classified

engineering design studies from the 1960s. The U.S. Department of Defense (DoD) developed

the system, which originally used 24 satellites. It became fully operational in 1995. Bradford

Parkinson, Roger L. Easton, and Ivan A. Getting are credited with inventing it.

Advances in technology and new demands on the existing system have now led to efforts to

modernize the GPS system and implement the next generation of GPS Block IIIA satellites and

Next Generation Operational Control System (OCX). Announcements from Vice President Al

Gore and the White House in 1998 initiated these changes. In 2000, the U.S. Congress

authorized the modernization effort, GPS III.

Fundamental

The GPS system concept is based on time. The satellites carry very stable atomic clocks that are

synchronized to each other and to ground clocks. Any drift from true time maintained on the

ground is corrected daily. Likewise, the satellite locations are monitored precisely. GPS receivers

have clocks as well—however, they are not synchronized with true time, and are less stable. GPS

satellites continuously transmit their current time and position. A GPS receiver monitors multiple

satellites and solves equations to determine the exact position of the receiver and its deviation

from true time. At a minimum, four satellites must be in view of the receiver for it to compute

four unknown quantities (three position coordinates and clock deviation from satellite time).

More detailed description

Each GPS satellite continually broadcasts a signal (carrier frequency with modulation) that

includes:

A pseudorandom code (sequence of ones and zeros) that is known to the receiver. By

time-aligning a receiver-generated version and the receiver-measured version of the code,

the time of arrival (TOA) of a defined point in the code sequence, called an epoch, can be

found in the receiver clock time scale

A message that includes the time of transmission (TOT) of the code epoch (in GPS

system time scale) and the satellite position at that time

Conceptually, the receiver measures the TOAs (according to its own clock) of four satellite

signals. From the TOAs and the TOTs, the receiver forms four time of flight (TOF) values,

which are (given the speed of light) approximately equivalent to receiver-satellite range

differences. The receiver then computes its three-dimensional position and clock deviation from

the four TOFs.

In practice the receiver position (in three dimensional Cartesian coordinates with origin at the

earth's center) and the offset of the receiver clock relative to GPS system time are computed

simultaneously, using the navigation equations to process the TOFs.

The receiver's earth-centered solution location is usually converted to latitude, longitude and

height relative to an ellipsoidal earth model. The height may then be further converted to height

relative the geoid (e.g., EGM96) (essentially, mean sea level). These coordinates may be

displayed, e.g. on a moving map display and/or recorded and/or used by other system (e.g.,

vehicle guidance).

User-satellite geometry

Although usually not formed explicitly in the receiver processing, the conceptual time

differences of arrival (TDOAs) define the measurement geometry. Each TDOA corresponds to a

hyperboloid of revolution (see Multilateration). The line connecting the two satellites involved

(and its extensions) forms the axis of the hyperboloid. The receiver is located at the point where

three hyperboloids intersect. It is sometimes incorrectly said that the user location is at the

intersection of three spheres. While simpler to visualize, this is only the case if the receiver has a

clock synchronized with the satellite clocks (i.e., the receiver measures true ranges to the

satellites rather than range differences). There are significant performance benefits to the user

carrying a clock synchronized with the satellites. Foremost is that only three satellites are needed

to compute a position solution. If this were part of the GPS system concept so that all users

needed to carry a synchronized clock, then a smaller number of satellites could be deployed.

However, the cost and complexity of the user equipment would increase significantly.

Receiver in continuous operation

The description above is representative of a receiver start-up situation. Most receivers have a

track algorithm, sometimes called a tracker, that combines sets of satellite measurements

collected at different times—in effect, taking advantage of the fact that successive receiver

positions are usually close to each other. After a set of measurements are processed, the tracker

predicts the receiver location corresponding to the next set of satellite measurements. When the

new measurements are collected, the receiver uses a weighting scheme to combine the new

measurements with the tracker prediction. In general, a tracker can (a) improve receiver position

and time accuracy, (b) reject bad measurements, and (c) estimate receiver speed and direction.

The disadvantage of a tracker is that changes in speed or direction can only be computed with a

delay, and that derived direction becomes inaccurate when the distance traveled between two

position measurements drops below or near the random error of position measurement. GPS

units can use measurements of the doppler shift of the signals received to compute velocity

accurately. More advanced navigation systems use additional sensors like a compass or an

inertial navigation system to complement GPS.

Non-navigation application

In typical GPS operation as a navigator, four or more satellites must be visible to obtain an

accurate result. The solution of the navigation equations gives the position of the receiver along

with the difference between the time kept by the receiver's on-board clock and the true time-of-

day, thereby eliminating the need for a more precise and possibly impractical receiver based

clock. Applications for GPS such as time transfer, traffic signal timing, and synchronization of

cell phone base stations, make use of this cheap and highly accurate timing. Some GPS

applications use this time for display, or, other than for the basic position calculations, do not use

it at all.

Although four satellites are required for normal operation, fewer apply in special cases. If one

variable is already known, a receiver can determine its position using only three satellites. For

example, a ship or aircraft may have known elevation. Some GPS receivers may use additional

clues or assumptions such as reusing the last known altitude, dead reckoning, inertial navigation,

or including information from the vehicle computer, to give a (possibly degraded) position when

fewer than four satellites are visible

GSM

The GSM technical specifications define the different elements within the GSM network

architecture. It defines the different elements and the ways in which they interact to enable the

overall system operation to be maintained.

The GSM network architecture is now well established and with the other later cellular systems

now established and other new ones being deployed, the basic GSM network architecture has

been updated to interface to the network elements required by these systems.

Despite the developments of the newer systems, the basic GSM system architecture has been

maintained, and the network elements described below perform the same functions as they did

when the original GSM system was launched in the early 1990s.GSM network architecture

elements

The GSM network architecture as defined in the GSM specifications can be grouped into four

main areas:

Mobile station (MS)

Base-Station Subsystem (BSS)

Network and Switching Subsystem (NSS)

Operation and Support Subsystem (OSS)

The different elements of the GSM network operate together and the user is not aware of the

different entities within the system.

A basic diagram of the overall GSM system architecture with these four major elements is shown

below:

Simplified GSM Network Architecture Diagram

Mobile station

Mobile stations (MS), mobile equipment (ME) or as they are most widely known, cell or mobile

phones are the section of a GSM cellular network that the user sees and operates. In recent years

their size has fallen dramatically while the level of functionality has greatly increased. A further

advantage is that the time between charges has significantly increased.

There are a number of elements to the cell phone, although the two main elements are the main

hardware and the SIM.

The hardware itself contains the main elements of the mobile phone including the display, case,

battery, and the electronics used to generate the signal, and process the data receiver and to be

transmitted. It also contains a number known as the International Mobile Equipment Identity

(IMEI). This is installed in the phone at manufacture and "cannot" be changed. It is accessed by

the network during registration to check whether the equipment has been reported as stolen.

The SIM or Subscriber Identity Module contains the information that provides the identity of the

user to the network. It contains are variety of information including a number known as the

International Mobile Subscriber Identity (IMSI).

Base Station Subsystem (BSS)

The Base Station Subsystem (BSS) section of the GSM network architecture that is

fundamentally associated with communicating with the mobiles on the network. It consists of

two elements:

Base Transceiver Station (BTS): The BTS used in a GSM network comprises the radio

transmitter receivers, and their associated antennas that transmit and receive to directly

communicate with the mobiles. The BTS is the defining element for each cell. The BTS

communicates with the mobiles and the interface between the two is known as the Um

interface with its associated protocols.

Base Station Controller (BSC): The BSC forms the next stage back into the GSM network. It

controls a group of BTSs, and is often co-located with one of the BTSs in its group. It manages

the radio resources and controls items such as handover within the group of BTSs, allocates

channels and the like. It communicates with the BTSs over what is termed the Abis interface.

Network Switching Subsystem (NSS)

The GSM system architecture contains a variety of different elements, and is often termed the

core network. It provides the main control and interfacing for the whole mobile network. The

major elements within the core network include:

Mobile Switching services Centre (MSC): The main element within the core network area of

the overall GSM network architecture is the Mobile switching Services Centre (MSC). The MSC

acts like a normal switching node within a PSTN or ISDN, but also provides additional

functionality to enable the requirements of a mobile user to be supported. These include

registration, authentication, call location, inter-MSC handovers and call routing to a mobile

subscriber. It also provides an interface to the PSTN so that calls can be routed from the mobile

network to a phone connected to a landline. Interfaces to other MSCs are provided to enable

calls to be made to mobiles on different networks.

Home Location Register (HLR): This database contains all the administrative information about

each subscriber along with their last known location. In this way, the GSM network is able to

route calls to the relevant base station for the MS. When a user switches on their phone, the

phone registers with the network and from this it is possible to determine which BTS it

communicates with so that incoming calls can be routed appropriately. Even when the phone is

not active (but switched on) it re-registers periodically to ensure that the network (HLR) is aware

of its latest position. There is one HLR per network, although it may be distributed across various

sub-centres to for operational reasons.

Visitor Location Register (VLR): This contains selected information from the HLR that enables

the selected services for the individual subscriber to be provided. The VLR can be implemented

as a separate entity, but it is commonly realised as an integral part of the MSC, rather than a

separate entity. In this way access is made faster and more convenient.

Equipment Identity Register (EIR): The EIR is the entity that decides whether a given mobile

equipment may be allowed onto the network. Each mobile equipment has a number known as

the International Mobile Equipment Identity. This number, as mentioned above, is installed in

the equipment and is checked by the network during registration. Dependent upon the

information held in the EIR, the mobile may be allocated one of three states - allowed onto the

network, barred access, or monitored in case its problems.

Authentication Centre (AuC): The AuC is a protected database that contains the secret key also

contained in the user's SIM card. It is used for authentication and for ciphering on the radio

channel.

Gateway Mobile Switching Centre (GMSC): The GMSC is the point to which a ME terminating

call is initially routed, without any knowledge of the MS's location. The GMSC is thus in charge of

obtaining the MSRN (Mobile Station Roaming Number) from the HLR based on the MSISDN

(Mobile Station ISDN number, the "directory number" of a MS) and routing the call to the

correct visited MSC. The "MSC" part of the term GMSC is misleading, since the gateway

operation does not require any linking to an MSC.

SMS Gateway (SMS-G): The SMS-G or SMS gateway is the term that is used to collectively

describe the two Short Message Services Gateways defined in the GSM standards. The two

gateways handle messages directed in different directions. The SMS-GMSC (Short Message

Service Gateway Mobile Switching Centre) is for short messages being sent to an ME. The SMS-

IWMSC (Short Message Service Inter-Working Mobile Switching Centre) is used for short

messages originated with a mobile on that network. The SMS-GMSC role is similar to that of the

GMSC, whereas the SMS-IWMSC provides a fixed access point to the Short Message Service

Centre.

CAN Bus in an Automobile

The Controller Area Network (CAN) is a serial communications protocol which efficiently supports

distributed real time control with a very high level of security. CAN Bus is a vehicle bus standard

designed to allow microcontrollers and devices to communicate with each other within a vehicle.

Its domain of application ranges from high speed networks to low cost multiplex wiring. In automotive

electronics, engine control units, sensors, anti-skid-systems, etc. are connected using CAN with bitrates

up to 1 Mbit/s. At the same time it is cost effective to build into vehicle body electronics, e.g. lamp

clusters electric windows etc. to replace the wiring harness otherwise required.

Salient Features of CAN protocol:

o Message based protocol Invented by Robert Bosch GmbH in 1980 for automotive applications.

o Asynchronous Serial Bus.

o Simple 2-wire differential bus.

o Absence of node addressing.

Message identifier specifies contents and priority

Lowest message identifier has highest priority

o Non-destructive arbitration system by CSMA with collision detection.

o Multi-master / Broadcasting concept.

o Sophisticated error detection & handling system.

CAN Bus Technology

CAN is a multi-master broadcast serial bus standard for connecting ECUs. Each node is able to send and

receive messages, but not simultaneously. A message consists primarily of an ID (identifier), which

represents the priority of the message, and up to eight data bytes. The improved CAN (CAN FD) extends

the length of the data section to up to 64 bytes per frame. It is transmitted serially onto the bus. This

signal pattern is encoded in non-return-to-zero (NRZ) and is sensed by all nodes. The devices that are

connected by a CAN network are typically sensors, actuators, and other control devices. These devices

are not connected directly to the bus, but through a host processor and a CAN controller. If the bus is idle

which is represented by recessive level (Logical 1), any node may begin to transmit. If two or more nodes

begin sending messages at the same time, the message with the more dominant ID (which has the higher-

order dominant - i.e., zero bit) will overwrite other nodes' less dominant IDs, so that eventually (after this

arbitration on the ID.) only the dominant message remains and is received by all nodes. This mechanism

is referred to as priority based bus arbitration. Messages with numerically smaller values of IDs have

higher priority and are transmitted first.

CAN Frames

A CAN network can be configured to work with two different message (or "frame") formats: the standard

or base frame format and the only difference between the two formats is that the "CAN base frame"

supports a length of 11 bits for the identifier, and the "CAN extended frame" supports a length of 29 bits

for the identifier All frames begin with a start the frame transmission. A CAN network can be configured

to work with two different message (or "frame") formats: the standard or base frame format and the

extended frame format. All frames begin with a start-of-frame (SOF) bit that denotes the start of CAN

has four frame types:

Data frame: a frame containing node data for transmission

Remote frame: a frame requesting the transmission of a specific identifier

Error frame: a frame transmitted

Overload frame: a frame to inject a delay between data and/or remote frame

Data frame

The data frame is the only frame for actual data transmission. There are two message formats:

Base frame format: with 11 identifier bits

Extended frame format: with 29 identifier bits

The CAN standard requires the implementation must accept the base frame format and may accept the

extended frame format, but must tolerate the extended frame format.

Control Flow at each CAN node:

START

Initialize ADC,CAN controller,ISR.

Is 20ms elapsed Or remote request received?

Read ADC, create message and set up frame ID.

Is transmit buffer full?

YES

NO

YES

NO

CAN Data Transmission:

START

Initialisation of I/O ports

Read Data from sensor

Initialisation of CAN Module

While (1)

Check ifCAN Bus is

Free?

Return Statement

Assign message ID

Transmit data on CAN bus

Delay

STOP

NO

NO

YES

YES

CAN Data Reception:

START

Initialisation of I/O ports

Initialisation of CAN

While (1)

Check ECU1 for

interruptupt

Return Statement

Check ECU2 forinterruptupt

Read ECU1 data

Read ECU2 data

Fan control / Buzzer alert

STOP

YES

NO