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13 Physical Layer
13.1 Diagnostic on K line
The Document "ISO 14230 - Part 1: Physical Layer" describes the physical layer, based on ISO 9141, on
which the diagnostic services are implemented. It is based on the physical layer described in ISO 9141-2,
but expanded to allow for vehicles with either 12 or 24 voltage supply.

13.1.1 Configuration

EDC7 support one wire (K line only) communication connection for diagnosis, test or maintenance. Vehicle
battery voltage, VB, power ground and signal ground shall be provided by the ECU or the vehicle to the
tester or to the signal transformer.
Line K is a bi-directional line. During fast initialization it is used to convey the wake up pattern from the
diagnostic tester to vehicle ECUs. After conveying this information, the K line is used for all other diagnostic
communications between tester and vehicle ECUs in both directions. This includes the completion of the
initialization sequence and all other communication services as described in this document.
The figure shows the system configurations:

Connector
(Vehicle)
K
Tester

ECU 1 ECU 2

Figure System configuration K line (The arrows indicate the direction of data flow)

If any ECU, either of one type or in combination are linked on a bus, the system designer shall ensure that
the configuration is capable of correct operation. For example, an initialization signal shall not cause more
than one ECU to respond simultaneously.
If lines K are used for purposes other than inspection, test and diagnosis, care shall be taken to avoid data
collision and incorrect operation in all modes.

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13.1.2 Signal Specifications

For proper operation of the serial communication , both ECU and diagnostic tester shall correctly determine
each logic state as follows:

• a logic "0 " is equivalent to a voltage level on the line of less than 20% of VB for transmitter, 30% VB for
receiver;
• a logic "1" is equivalent to a voltage level on the line of greater than 80% VB for transmitter , 70% Vb for
receiver .

In addition, the slope times shall be less than 10% (15%) of the bit time. The slope times are defined as the
time taken for the voltage to change from 20% to 80% VB ,and from 80% to 20% VB for transmitters.
Voltage levels between 30% and 70% of VB may be detected as either logic "0" or logic "1 ". NRZ coding is
used. The bit time is defined as half the time between the 50% VB levels of successive rising or falling
edges of alternating " 1 " and " 0 " bits.
The figure below illustrates the worst case on signal levels:

Transmitter VB Receiver
VB
100%

Logic "1" sent 80%

70% Logic "1" received

Margins

30% Logic "0" received

Logic "0" sent 20%

0%

Ground

Figure signal levels for K line

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13.1.3 Communication Specification

The configuration is shown schematically in the following figure:

Vehicle Diagnostic Tester

VB

ECU
Reading Line K

"1"
"1" or
Ι
or "0"
C
C C TE
"0" ECU OBW
Ground

Figure Detailed system configuration K line

The capacitance contribution of the diagnostic tester and associated cables are termed by CTE The
capacitance contribution of the on-board wiring is termed by COBW . The sum of the input capacitance of all
the ECUs on the bus is defined thus:
n
CECU = ∑ CECU i where n is the number of ECUs on the bus.
i =1

Values for CECU and COBW must be selected such that

CECU + COBW ≤ 7.2nF and CTE ≤ 2nF

(CECU + COBW ≤ 5.0nF and CTE ≤ 2nF for 24V vehicle battery voltage systems)
These values are derived from the circuit resistance and baud rate tolerances, allowed slope times and
switching thresholds and assuming a maximum communication speed of 10,4 KB. If a higher or lower
maximum communication speed is chosen then the designer will reduce or increase the allowed
capacitance accordingly . The formula to be used is described in ISO 9141.

13.1.4 Requirements Of The Diagnostic Tester

13.1.4.1 Minimum Functional Requirements

The diagnostic tester shall be capable of supporting the initialization methods and the communication
protocol described in ISO 14230-2.

13.1.4.2 Electrical Specifications

(First values are for vehicles with nominal 12V supply, values in parentheses are for 24V vehicle battery
voltage systems)
These specifications shall apply over a working temperature range of 0 ∞C to 50 ∞C.
The following specifications shall apply to nominal 12V (24V) systems for which the diagnostic tester shall
operate correctly in the range 8 V to 16 V (16 V to 32 V) of the vehicle battery voltage VB. Manufacturers of
diagnostic testers are encouraged to extend the limits of correct operation for vehicle battery voltage VB
and working temperature.
For line K of the diagnostic tester not connected to an ECU, it shall be internally pulled up to VB via a
nominal 510 Ω (1KΩ) resistor.

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Transmission state
• At logic " 1 " the diagnostic tester shall have an equivalent voltage source greater than 90 % VB ,sourced
from the vehicle battery supply VB, and an equivalent resistance of 510 Ω ± 5 % (1kΩ ± 5 % ).
• At logic " 0 " the diagnostic tester shall have an equivalent voltage of less than 10 % of VB, at a
maximum sink current of 100mA.

Receiving state
• The equivalent resistance on the line K of the diagnostic tester shall be 510 Ω ± 5% (1kΩ ± 5 % ) to VB.
The diagnostic tester will maintain fast initialization and communication baud rates to ± 0,5 % of nominal
values where specified by the protocol. Where determined by measurement the baud rate shall be
maintained to ± 1%.
For each byte the diagnostic tester shall be capable of determining the status of any bit, the transitions of
which are shifted by not more than 30 % of the bit time relative to their calculated position in time.
The diagnostic tester shall not transfer to the open lines K any voltage higher than VB or 40V , whichever is
the lower, or any voltage which is lower than -1V. This includes suppression of voltage excursions of VB as
detailed in ISO/TR 7637
The diagnostic tester shall expect a resistance of at least 5kΩ (10kΩ ) to vehicle signal ground and at least
10kΩ ( 20kΩ ) to VB on lines K when connected to the vehicle.
The total capacitance of the diagnostic tester and its cable and connector shall not exceed 2nF.

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13.2 Diagnostic on CAN

The Document "ISO 15765 - Part 4" describes the physical layer, based on ISO 11898.

13.2.1 Configuration

EDC7 supports two wire communication connection via Contoler Area Network (CAN) for diagnosis, test or
maintenance. Vehicle battery voltage, VB, power ground and signal ground shall be provided by the ECU or
the vehicle to the tester or to the signal transformer.
The CAN is a bi-directional bus system. The CAN may be used for all communications between tester and
vehicle ECUs in both directions. This includes all communication services as described in this document.
No initialisation is necessary for diagnostic on CAN.

The figure shows the system configurations:

Connector
(Vehicle) CANH

Tester

CANL

ECU 1 ECU 2

Figure System configuration CAN (The arrows indicate the direction of data flow)

If any ECU, either of one type or in combination are linked on a bus, the system designer shall ensure that
the configuration is capable of correct operation. For example, a diagnostic message on CAN shall not
cause more than one ECU to respond simultaneously.
If the CAN is used for purposes other than inspection, test and diagnosis, care shall be taken to avoid data
collision and incorrect operation in all modes.

13.2.2 Signal specifications

The supports the following baudrates for diagnostic on CAN:

- 250 kBit/s

- 500 kBit/s

This section specifies the required CAN bit timing parameter settings for the external test equipment based
on the timing parameter definitions in ISO 11898. All given requirements are specified for operation at 250
kBit/s and 500 kBit/s. The external test equipment CAN controller shall support enhanced bit timing.

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Nominal bit time

ISO 11898 terms: Sync_Seg Prop_Seg Phase_Seg1 Phase_Seg2

ISO 15765-4 terms: TSYNCSEG TSEG1 TSEG2

Nominal Sample Point Position (SP)

in single data sampling mode

Figure Partitioning of CAN bit time

The CAN bit timing parameter values are based on the ISO 11898 terms and definitions:
tSYNCSEG = Sync_Seg = 1 * tQ
tSEG1 = Prop_Seg + Phase_Seg1 = tBIT - tSYNCSEG - tSEG2
tSEG2 = Phase_Seg2
tSJW = Resynchronisation Jump Width
tBIT = tB (nominal bit time)
tQ = time quantum
SP = Nominal Sample Point Position = (1 - tSEG2/tBIT) * 100 %
Compliance with the nominal bit time tolerance requirement specified in the following sections is directly
dependent on the CAN system clock tolerance of the external test equipment and the programmed nominal
bit time value. In a typical CAN controller, the nominal bit time value must be an integer multiple of its
system clock periods. When the programmable nominal bit time value is set exactly to the required nominal
bit time value, accuracy is only affected by the system clock tolerance. Otherwise, the accuracy is
dependent upon both the deviation of the programmed bit time value from the nominal bit time value and
the system clock tolerance. The contributions from drift or aging of the system clock source and
contributions from inability to achieve the desired nominal bit time value are additive; the bit time tolerance
specification must be met after consideration of both.

13.2.2.1 Nominal baudrate 250 kBit/s

The following table specifies the allowed CAN bit timing parameter values for a baudrate of 250 kBit/s. The
external test equipment shall operate in single data sampling mode.
Tolerance of the external test equipment nominal baudrate: 250 kBit/s +/- 0.15%

Term Min. Nominal Max.

tBIT_RX 3980 ns 4000 ns 4020 ns
tBIT_TX 3994 ns 4000 ns 4006 ns
tQ ----- ----- 250 ns
∆f ----- ----- 0.15%

NOTE The min. and max. values of the nominal bit time tBIT_RX are worst-case values for the reception of bits from
the CAN bus based on a nominal baudrate tolerance of +/- 0.5%. The min. and max. values of the nominal bit
time tBIT_TX are worst-case values for the transmission of bits onto the CAN bus based on the specified
external test equipment nominal baudrate tolerance of +/- 0.15%.

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The following table contains the only allowed CAN bit timing parameter values for the external test
equipment based on standard time quanta (tQ) and the timing parameters listed above.

tQ tSJW tSEG1 tSEG2 Nominal Sample Point

Position
200 ns 600 ns 3000 ns 800 ns 80%
250 ns 750 ns 3000 ns 750 ns 81.25%

NOTE The nominal sample point position is specified relative to one (1) bit time.

13.2.2.2 Nominal baudrate 500 kBit/s

The following table specifies the allowed CAN bit timing parameter values for a baudrate of 500 kBit/s. The
external test equipment shall operate in single data sampling mode.
Tolerance of the external test equipment nominal baudrate: 500 kBit/s +/- 0.15%

Term Min. Nominal Max.

tBIT_RX 1990 ns 2000 ns 2010 ns
tBIT_TX 1997 ns 2000 ns 2003 ns
tQ ----- ----- 125 ns
∆f ----- ----- 0.15%

NOTE The min. and max. values of the nominal bit time tBIT_RX are worst-case values for the reception of bits from
the CAN bus based on a nominal baudrate tolerance of +/- 0.5%. The min. and max. values of the nominal bit
time tBIT_TX are worst-case values for the transmission of bits onto the CAN bus based on the specified
external test equipment nominal baudrate tolerance of +/- 0.15%.

The following table contains the only allowed CAN bit timing parameter values for the external test
equipment based on standard time quanta (tQ) and the timing parameters listed above.

tQ tSJW tSEG1 tSEG2 Nominal Sample Point

Position
100 ns 300 ns 1500 ns 400 ns 80%
125 ns 375 ns 1500 ns 375 ns 81.25%

NOTE The nominal sample point position is specified relative to one (1) bit time.

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13.2.3 Electrical specifications

This section specifies the required electrical parameters to be fulfilled by the external test equipment. The
requirements are separated into requirements for the external test equipment CAN interface and the
external test equipment cable.

13.2.3.1 External test equipment CAN interface

This section specifies the required electrical parameters to be fulfilled by the external test equipment CAN
interface which does not include the cable.

Figure External test equipment electrical parameters

The external test equipment capacitive load does not include the capacitive load of the external test
equipment cable. These values only apply to the CAN interface of the external test equipment Hardware,
with the exception of the AC termination. These values are seen during the recessive state when the
external test equipment is disconnected from the cable, and the AC termination is not inserted yet.

Term Min Nominal Max Description

CDIFF ----- ----- 50 pF CAN_H to CAN_L
CCAN_H, CCAN_L ----- ----- 100 pF CAN_H/CAN_L to ground potential

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The external test equipment propagation delay does not include the cable propagation delay. This value
only applies to the CAN interface of the external test equipment Hardware. This requirement is based on the
most critical timing when operating at the baud rate of 500 kbit/s. The external test equipment propagation
delay (loop delay) includes all delays that can be caused by the CAN interface of the external test
equipment (e.g. CAN transceiver propagation delays, CAN controller propagation delays).

Term Min Nominal Max Description

tTOOL ----- ----- 390 ns Loop Delay of external test equipment

13.2.3.2 CAN bus termination

This section specifies the termination requirements to be fulfilled by the external test equipment.

Figure External test equipment CAN bus termination

There shall not be any termination resistor between the CAN conductors CAN_H and CAN_L in the external
test equipment for the adaptation to the physical media impedance. The external test equipment shall be an
unterminated node on the CAN bus to which it is connected. The external test equipment shall have an AC
termination for the purpose of minimizing reflections on the CAN bus. Reflections on the CAN bus occur in
the external test equipment CAN interface because of the fact, that the external test equipment is required
to not adapt to the physical media impedance via a physical media termination resistor.

Term Min Nominal Max Description

R1, R2 90 Ohm 100 Ohm 110 Ohm Resistor of the AC-Termination

C1, C2 470 pF 560 pF 640 pF Capacitor of the AC-Termination

NOTE R1 = R2 and C1 = C2.

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13.2.3.3 External test equipment cable

The external test equipment cable shall provide interconnection between the vehicle connector and the CAN
interface of the external test equipment. The external test equipment cable length is defined to be the length
of the cable between the vehicle connector and the external test equipment CAN interface. This length shall
not exceed 5 meters.

The cable propagation delay does not include the external test equipment propagation delay. This value
only applies to the cable. This requirement is based on the most critical timing when operating at the
baudrate of 500 kbit/s. The cable propagation delay is defined as a one-way delay (from the vehicle
connector to the external test equipment CAN interface) and shall not exceed 27,5 ns.

The following configuration requirements apply to the external test equipment cable:
 No other wires shall be twisted with either CAN conductor(s) CAN_H and CAN_L. Twisting of the CAN
conductors with Signal ground is allowed.

 The CAN_H and CAN_L conductors shall have the same length and traverse the same path for the
entire distance.

 CAN_H and CAN_L conductor(s) shall not be included in a bundle which contains radiating wires which
induce more than 0.5 volts noise modulation on either CAN conductor relative to Signal ground.

 The cable shall be shielded if the external test equipment cable length exceeds 1 m. The shield shall be
connected to the Chassis ground pin of the cable side of the vehicle connector.

NOTE There are no requirements for twisting.

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