AN602 データシートの表示（PDF） - Vishay Semiconductors

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AN602

Driver ICs for Automotive Diagnostic Communications Meet ISO 9141 Standards

Vishay Semiconductors 

Physical Layer

Figure 5 shows the physical layer capacitance of the ISO 9141

communication scheme.

CTE

COBW

CECU

= Tester and Cables

= On-Board Wiring

= Sum of all ECU Input Capacitance

where CECU + COBW is less or equal to 7.6 nF and CTE is less or

equal to 2 nF.

The capacitance of the K or L Lines with respect to GND can be

no greater than 500 pF.

The resistance of the K and L Line is specified with respect to their

State.

Logic 1"/Receiving

K (ECU to GND)

L (ECU to GND)

Logic 0"

w 50 kW v 110 W

w 50 kW N/A

Any resistance placed between the K or L Line and Vb must have

a value greater than 100 kW.

Data Rate

The maximum data rate will vary depending on the number of

ECUs and length of cabling. ISO 9141 specifies a maximum bus

capacitance of 9.6 nF. Figure 6 shows the maximum data rate

versus capacitance.

Data Format and Protocol

This application note will only give a general outline of the ISO

9141 communication scheme. The user is advised to read the

actual ISO 9141 specification.

AN602

Vishay Siliconix

Initialization

Before initialization, the K-Line is a Logic 1 for the time period of

the address to be transmitted. The diagnostic tester then sends

an 8-bit address on the K and L lines (one start, 8-bit address, one

stop) to the ECU.

Transmission

Before transmitting, the K-Line is a Logic 1 for the time period of

the word to be transmitted. An alternate bit pattern is then sent to

synchronize the receiver and set the baud rate. After the

transmission of the synchronization pattern, two key words are

sent to the tester to identify the form of the data and the hardware

configuration.

When the last key word is sent by the ECU, the tester will echo

back the logic inversion of the last word back to the ECU. When

this is complete, the ECU will transmit the logic inversion of the

initialization address.

Conclusion

Vishay Siliconix’ ISO 9141 bus driver series is produced to save

the automotive designer time and space while improving the

overall reliability of the diagnostic system. Each driver exceeds

the ISO 9141 transient and data requirements, as well saving

significant space overall to a discrete solution. With these factors

considered, it should reduce manufacturing, building and design

costs, and produce a very economical solution to automotive bus

interfacing.

Reference

ISO 9141 - CARB Road Vehicles * Diagnostic Systems.

N425/rev. Jan. 91

Vehicle (Clause 9)

VB

Diagnostic Tester

(Clause 8)

Reading

“1”

or

“0”

ECU

Line K

Reading

I

“1”

or

C

C

C

“0”

ECU ECU

TE

GND

FIGURE 5. Communication Schematic

Document Number: 70573

16-Jan-01

1000

100

10

Assumes VBAT above 9 V,

and a capacitive load

1

0.1

1

10

100

Capacitance (nF)

1000

10,000

FIGURE 6. Maximum NRZ Data Rate with Capacitive

Load Si924X with 510-W Load

www.vishay.com

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