Global Sources
EE Times-India
Stay in touch with EE Times India
 
EE Times-India > Networks
 
 
Networks  

Automotive networking systems proliferate through components

Posted: 16 Mar 2004     Print Version  Bookmark and Share

Keywords:Embedded 

PDF document

By Ross Bannatyne

Manager, Americas Region

Distribution Market Operation

Motorola Semiconductor

Products Sector

Since microcontrollers with

controller area network (CAN)

hardware were introduced in

1993, there has been a steady

growth in the popularity of

CAN-based systems. In the 10

years since, CAN is now firmly

establishedasaleadingautomo-

tive and industrial networking

protocol. This growth can be

attributed to a few things.

First, there was good initial

momentum as the developer

was Robert Bosch GmbH, a

huge global automotive, con-

sumer and industrial goods

manufacturer. Second, there

was the widespread availability

of low cost hardware such as

microcontrollers and trans-

ceiver chips to support the pro-

tocol. Finally there was a self-

reinforcing phenomenon that

occurs when increasing vol-

umes and lowering hardware

costs are in effect.

This article was inspired by

yet another milestone in the

CAN story, the availability of

the industry's smallest, lowest

cost CAN microcontrollers.

This is significant as it reduces

further the entry cost level to

CANsystemsandopenupmore

applications that will be net-

worked via a CAN node. While

lower cost networks such as lo-

cal interconnect network (LIN)

are often considered because of

their low implementation cost,

the continued cost reductions

of CAN systems have certainly

invaded this space as the ratio

of robustness to cost is very at-

tractive to many designers.

Networking in the automobile

Although the biggest growth in

the number of CAN applica-

tionsisprobablynowtheindus-

trial market segment, CAN's

heritage is clearly automotive.

Aside from the automobile,

CANs are used in systems such

as building automation, cli-

mate and lighting controls,

airconditioning, alarm sys-

tems, sprinkler systems, eleva-

tors, escalators, vending ma-

chines and motor controls. The

range of applications will con-

tinue to increase in the future--

anything that needs a robust,

reliable low-cost network will

become a candidate to increase

the number of CAN nodes in

existence from the estimated

150 million today.

Themainmotivationbehind

networking the vehicle was to

address the increases in cost

and weight that the addition of

many electronic systems

brings. Each system typically

includeditsownwiringharness

that connects to the ECU, bat-

tery, instrumentation panel

controls,sensorsandactuators.

The wiring consisted of sepa-

rate copper wires that add a sig-

nificant amount of weight to

the vehicle. Before the intro-

duction of multiplexed net-

works, a luxury vehicle could

include over a mile length of

insulated wiring consisting of

around 1,500 individual wires

andover2,000terminals.Aside

from being expensive and

heavy, it was becoming impos-

sible to even feed the large wir-

ing harness into the door.

The conventional wiring

system was also a source of

many reliability issues. Like all

electronic systems, the more

interconnections that were

present, the more opportuni-

ties there were for mechanical

interfacing problems. It was no

surprise that many field fail-

ures were the result of the in-

terconnect issues.

The solution to the problem

was to replace all the individual

wiring systems, where possible,

with a multiplexed serial com-

municationsnetwork.Theoreti-

cally,itwouldbeasinglebussys-

tem that link up all the related

systems in the vehicle. This

would reduce number of wiring

harnesses, weight, cost, assem-

bly time, and would promote

better reliability through re-

duced number of interconnec-

tions. A simplified diagram is

shown in Figure 1 which com-

pares a door control system us-

ing a conventional wiring and a

multiplexed wiring system. The

doorshownonthelefthandside

of the illustration uses many

more wires to connect up the

functions door controls and

must be fed through the door.

The door shown on the right

handsideoftheillustrationuses

amultiplexedwiringsystemthat

isconnectedtothecontrollerin

the instrumentation system.

The multiplexed wiring system

uses considerably fewer wires

and connections.

Vehicle network messages

are transmitted as serial pack-

ets of information. Usually

they consist of three fields--a

header, the destination ad-

dress for the packet; data, usu-

ally three to 12 bytes in length;

and error correction, a cyclic

redundancy code or checksum

Automotive networking systems proliferate

through components

to ensure that the packet has

not been corrupted.

The network can also be

used to improve the diagnostic

capabilityofthevehicle.Rather

than having to locate a fault by

debugging many different sys-

tems, a networked vehicle will

usually have one port, often

under the dashboard, to which

diagnostic equipment can be

connected. As electronic sys-

tems are networked together,

this port allows access to all the

electronic systems in the auto-

mobile. Faults or status infor-

mation can be acquired more

easily than examining several

different independent systems.

CAN microcontrollers

Figure2illustratesthebasicre-

quirementsofamicrocontroller-

based CAN controller. This de-

vice is the basic element of a

CAN-based system and is used

at every node in the network.

This hardware is commonly in-

cludedasamoduleonintelligent

devicessuchasmicrocontrollers

that are used to control the

system that is connected to the

network.

The module will have a

simple interface to the CPU so

that it can be controlled easily

bythesystemsoftware.Thereis

a buffering stage such that data

can be transferred seamlessly

and synchronously from the

CPU onto the CAN bus. The

protocol handling stage pack-

ages the data into the format

Battery

Control

Control

ControlRF input

Output

(Switch on door)

Output Output

Battery

Control

RF input

Output Output Output

Control

Window

lift

controller

Door

lock

controller

Electric

mirror

controller

Window

lift

controller

Door

lock

controller

Electric

mirror

controller

Figure 1: Multiplexed wiring system uses considerably fewer wires and connections compared to conventional wiring system.

thatisrequiredbytheCANbus,

and finally this data is trans-

ferred to a physical layer stage

that is usually contained in a

separate transceiver chip.

The purpose of the trans-

ceiver is to convert the digital

information that is used on the

controller chip to a robust

higher voltage signal that is re-

quiredonthephysicalwiring.In

addition, the CAN controller

will include some on-board cir-

cuitry that will detect, identify

and report errors, store mes-

sages,generateinterruptstothe

systemsandarbitratethesystem

with as little intervention from

theCPUaspossible.Thismeans

that the microcontroller's main

taskistocontrolthenodeappli-

cation, for example controlling

a motor, rather than spend re-

sources on managing the CAN.

Probably the single most im-

portant factor in the success

and popularity of the CAN pro-

tocolhasbeentheavailabilityof

lowcostelectroniccomponents

to build CAN-based systems. It

is significant that new compo-

nentsarecontinuallyproduced,

every new generation driving

the price down further. In

March 2003, a new milestone

for CAN based systems was set

with the production of two new

CAN microcontrollers that al-

low the production of the low-

est cost CAN nodes yet. These

are the MC68HC908GZ8 and

the MC68HC908GZ16 micro-

controllers. Both devices in-

clude identical technical fea-

turesbutdifferintheamountof

on-chip flash EEPROM pro-

gram memory that they offer.

The MC68HC908GZ8 and

the MC68HC908GZ16 are

based upon Motorola's high

performance 8bit HC08 archi-

tectureandarecompatiblewith

the 68HC05 microcontroller

family (which was the first 8bit

microcontroller to include a

CAN controller back in 1993).

The devices feature CAN mod-

uleswith8KBand16KBofflash

memory, respectively.

The modules shown on the

diagram are the different cir-

cuits of the microcontroller

that are used to control the

overall system. The CPU is

shown as a block along with the

flash program memory and the

RAM that is used for changing

data. The PLL circuit is used

to control the on-chip clock

alongwiththeclockgeneration

module (CGM). The actual

CAN controller module is

MSCAN08. This nomenclature

represents the Motorola Scal-

able CAN system, intended for

the CPU08 processor. On the

right hand side of the block dia-

gram, the keyboard interrupt

(KBI) system, 4-channel/10bit

ADC, enhanced serial commu-

nicationsinterface(ESCI),SPI,

2 x 2-channel/16bit timers and

GPIO pins are shown. Typically

these modules would be con-

necteduptopartsofthecontrol

system that could be motors,

relays, solenoids and other ac-

tuators and sensors.

The flash program memory

of the microcontroller is an

important feature. Flash

EEPROM is a relatively low-

cost (compared with the stan-

- Access control and status registers

- Access to buffers

- Interrupt and error types

- Store incoming and outgoing messages

- Only interrupt CPU with relevant messages

- Predictable message transmission

- Error detection

- Arbitration detection

- Bit monitoring/stuffing

- Current and voltage control for bus

- Absorb transients

- Signal bus (line) faults and correct

Simple user interface to CPU

Message filtering and buffering

Protocol handling

Physical layer interface

CPU

interface

CAN

transmit/

receive

engine

Message

filtering+

buffering

Control

+ status

H/W

errors

MCU

Tx

RxPhysical

interface

CAN bus

CANH

CANL

dard byte-erasable EEPROM)

type of memory which may be

reprogrammed easily in the

field. The main difference be-

tween byte-erasable EEPROM

and flash is that the flash

memory array may be erased as

a block. This allows a smaller

sized array as less addressing

logic is required and it also al-

lows software changes faster.

Control system manufactur-

ersoftenwishtorevisesoftware

in the field. Unless there is a

method of reprogramming the

memory array remotely, typi-

cally this problem requires the

sealed control unit circuit

board to be removed and re-

placed. This is a time-consum-

ing and expensive process for

the manufacturer, not to men-

tion a greater inconvenience to

all concerned. Flash EEPROM

provides the technology which

allows such field revisions. In

addition, as the ECU would be

connected to a multiplex bus

system, this bus can be used to

transmit the software changes

to the ECU. To facilitate this, a

laptop computer hosting the

revised software could be con-

nected to the multiplex bus

port at a convenient location.

The physical-layer portion

of the system is usually imple-

mented in a separate chip. This

gives the designer flexibility

over the characteristics of the

network that is being imple-

mented. To complement the

MC68HC908GZ8/GZ16, the

MC33989 system basis chip is

recommended. This chip pro-

vides the CAN transceiver as

well as additional functionality

that is always required in the

system such as power supply.

Itlooksclearthatthegrowth

ofCAN-basedsystemsthrough-

out the 1990s is set to continue

in the next decade, as suppliers

of the hardware controller ele-

ments push down costs and of-

fer a variety of products to sup-

port CAN-based systems. CAN

has truly become a standard--

this means that there is a huge

installed base and educated

community of designers who

willuseCANaslongasitiscost-

effective to do so. New control-

ler chips will continue to sup-

port CAN for the future.

CGM

4-channel

10bit ADC

KBIHC08 CPU

ESCI

2x2-channel

16bit

timer

16KB/8KB

Flash

1KB RAM

MSCAN08

SPI

Up to

21 GPIOs

PLL

32QFP

48LQFP

Figure 2: CAN-based microcontroller.

Figure 3: A block diagram of

MC68HC908GZ8/GZ16.





Comment on "Automotive networking systems prolif..."
Comments:  
*  You can enter [0] more charecters.
*Verify code:
 
 
Webinars

Seminars

Visit Asia Webinars to learn about the latest in technology and get practical design tips.

 

Go to top             Connect on Facebook      Follow us on Twitter      Follow us on Orkut

 
Back to Top