ISO 16844-3:2004

INTERNATIONAL ISO
STANDARD 16844-3
First edition
2004-11-01


Road vehicles — Tachograph systems —
Part 3:
Motion sensor interface
Véhicules routiers — Systèmes tachygraphes —
Partie 3: Interface de capteur de mouvement





Reference number
ISO 16844-3:2004(E)
©
ISO 2004

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ISO 16844-3:2004(E)
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ISO 16844-3:2004(E)
Contents Page
Foreword. iv
Introduction . v
1 Scope. 1
2 Normative references. 1
3 Terms and definitions. 1
4 Symbols and abbreviated terms. 3
5 Connector. 4
5.1 Dimensions and pin allocation . 4
5.2 Electrical specification. 5
6 Cable. 8
7 Interface protocol. 9
7.1 Transmission. 9
7.2 Motion sensor state at the end of production. 12
7.3 Instructions. 13
7.4 Initialization of communication between motion sensor and vehicle unit . 13
7.5 Communication of motion sensor and vehicle unit in normal use. 18
7.6 Read information. 21
8 Options. 31
8.1 Direction information. 31
8.2 Additional direction information in the MF byte . 32
Bibliography . 34


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ISO 16844-3:2004(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 16844-3 was prepared by Technical Committee ISO/TC 22, Road vehicles, Subcommittee SC 3,
Electrical and electronic equipment.
ISO 16844 consists of the following parts, under the general title Road vehicles — Tachograph systems:
 Part 1: Electrical connectors
 Part 2: Recording unit, electrical interface
 Part 3: Motion sensor interface
 Part 4: CAN interface
 Part 5: Secured CAN interface
 Part 6: Diagnostics
 Part 7: Parameters
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ISO 16844-3:2004(E)
Introduction
ISO 16844 supports and facilitates the communication between electronic units and a tachograph; the
[1] [2]
tachograph being based upon Council Regulations (EEC) No. 3820/85 and (EEC) No. 3821/85 and their
[3] [4]
amendments Council Regulation (EEC) No. 2135/98 and Commission Regulation (EC) No. 1360/2002 .
Its purpose is to ensure the compatibility of tachographs from various tachograph manufacturers.
The basis of the digital tachograph concept is a recording unit (RU) that stores data related to the activities of
the drivers of a vehicle on which it is installed. When the RU is in normal operational status, the data stored in
its memory are made accessible to various entities such as drivers, authorities, workshops and transport
companies in a variety of ways: they may be displayed on a screen, printed by a printing device or downloaded
to an external device. Access to stored data is controlled by a smart card inserted in the tachograph.
In order to prevent manipulation of the tachograph system, the speed signal sender (motion sensor) is
provided with an encrypted data link.
A typical tachograph system is shown in Figure 1.


Key
1 positive supply
2 battery minus
3 speed signal, real time
4 data signal in/out
Figure 1 — Typical tachograph system
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INTERNATIONAL STANDARD ISO 16844-3:2004(E)

Road vehicles — Tachograph systems —
Part 3:
Motion sensor interface
1 Scope
This part of ISO 16844 specifies the physical and data link layers of the electrical interface connecting a
motion sensor to a vehicle unit, used in tachograph systems in road vehicles to perform speed signal
transmission and data interchange.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 15170-1, Road vehicles — Four-pole electrical connectors with pins and twist lock — Part 1: Dimensions
and classes of application
ISO/IEC 10116, Information technology — Security techniques — Modes of operation for an n-bit block cipher
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
check sum
sum (two byte value) of the bytes pointed out at the corresponding location
3.2
direction of movement
bit 6 of byte MF showing whether the vehicle moving direction is forward or reverse
3.3
direction of movement ON
bit 7 of Byte MF showing whether the additional direction information is available or not
3.4
identification key
key necessary for Initialization of a motion sensor, not stored in the sensor memory
NOTE The identification key is derived by adding a constant control vector of the value
48 21 5F 00 03 41 32 8A║ 00 68 4D 00 CB 21 70 1D hexadecimal on the master key (K =K XOR CV).
l
ID
3.5
inter byte timing
possible pause between two bytes of a message
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ISO 16844-3:2004(E)
3.6
header
first four bytes of a message containing sync-byte, target, STX and length of the message
3.7
key
master key
key necessary for Initialization of a motion sensor, not stored in the sensor memory
3.8
pairing key
key only used during the pairing sequence
NOTE Every pairing key is unique to the motion sensor to which it belongs.
3.9
reset
restart of the motion sensor processing unit program
3.10
RxD_in
signal within the motion sensor to the RxD input of the processing unit
3.11
sensor signal
frequency signal proportional to the speed within the motion sensor
3.12
session key
key used for messages to be encrypted
NOTE Every session key is unique to a special motion sensor and the vehicle unit to which it belongs.
3.13
tail
last two bytes of a message containing ETX and LRC
3.14
triple DES
multiple encryption or decryption of plain text or cipher text with different keys
NOTE 1 Encryption: first, the plain text is encrypted using a first key, then it is decrypted using a second key, and then
it is encrypted again using a third key.
NOTE 2 Decryption: first, the cipher text is decrypted using the third key, then it is encrypted using the second key, and
then it is decrypted again using the first key.
3.15
two-key triple DES
encryption algorithm similar to triple DES where the third key used is equal to the first one
3.16
TxD_out
signal within the motion sensor from the TxD output of the processing unit
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ISO 16844-3:2004(E)
3.17
vehicle unit
recording equipment excluding the motion sensor and its connecting cables
NOTE The vehicle unit can either be a single unit or several units distributed in the vehicle, as long as it complies
with the security requirements of [1], [2] and [3].
3.18
voltage monitor
hardware function that detects a drop of the supply voltage below a defined level
3.19

K′
P
key derived from the pairing used to encrypt the pairing data
4 Symbols and abbreviated terms
CS check sum
Cs high byte of CS
high
Cs low byte of CS
low
CV control vector
CVPI check value previous instruction
D data for authentication
A
DES data encryption standard
D data of file selected
Fs
DON direction of movement On
DM direction of movement
D data of sensor (encrypted, i.e. two-key triple DES)
S
EXT end of text marker
K master key
K identification key
ID
K pairing key
P
K sessions key
S
LSB least significant byte
LRC longitudinal redundancy check
MF multi function byte
MSB most significant byte
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ISO 16844-3:2004(E)
NARA new audit record available
N extended serial number
S
P pairing data
D
STX start of text
VU vehicle unit
XOR arithmetical exclusive OR
5 Connector
5.1 Dimensions and pin allocation
The connector used (see Figure 2) shall be according to ISO 15170-1, with coding No. 1, application class K3
2
(contact temperature range −40 °C to +140 °C, max. acceleration of vibrations 300 m/s ).
The pin allocation shall be in accordance with Table 1.

Key
1 to 4 pin Nos.
Figure 2 — Marking zone at fixed or free connector — Code 1
Table 1 — Pin allocation
Pin No. Function
1 Positive supply
2 Battery minus
3 Speed signal, real time
4 Data signal, in/out

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ISO 16844-3:2004(E)
5.2 Electrical specification
5.2.1 Electrical requirements
The allocated connector function shall be in accordance with Table 2 and valid within the temperature range
−40 °C to +135 °C.
Table 2 — Electrical requirements of allocated connector function
Electrical requirements
Pole
Function Parameter Remark
No.
min. typical. max.
b
1 Positive Voltage 6.5 V — 9 V Reverse voltage protected
supply
Current I 15 Total unit current without direction signal current,
S
— —
mA see Clause 8.
2 Battery minus — — — — See ISO 16844-2.
b
3 Speed signal U — — 0,8 V I = 250 µA
low
a
real time
U U
high pos sply b
— — I = −150 µA
–1,5 V
Rise time Test condition: External pull up resistor 22 kΩ to
— 50 µs —
(10 % to 90 %) positive supply (U ); U = 6,5 V; external
pos sply pos sply
capacitor 2 nF to battery minus.
Fall time
— 10 µs —
(90 % to 10 %)
Frequency <1,6
— — —
kHz
b
4 Data signal U — — 1,2 V I = −1 mA
low in
a
in/out
b
U 5,2 V — — I = − 0,5 mA
high in
b
U — — 1 V I = 1 mA
low out
b
U 5,4 V — — I = –20 µA
high out
Rise time Test condition: External pull up resistor 10 kΩ to
— 110 µs —
(10 % to 90 %) positive supply (U ); U = 6,5 V; external
pos sply pos sply
capacitor 5 nF to battery minus.
Fall time
— 10 µs —
(90 % to 10 %)
Baud rate — 1200 Baud — Accuracy ± 3 %
a
Outputs shall be short circuit protected up to 28V and 1 min.
b
All values measured relative to pin 2.

5.2.2 Block diagram data signal, in/out
Figure 3 shows a block diagram of the data interface hardware. If no communication takes place, the state of
pin 4 shall be high. The incoming signal at pin 4 shall be filtered before it is used as an input signal to the
processing unit.
The data TxD_out shall only be transmitted if the voltage monitor shows that the supply voltage is within the
specified range. See also 7.5.3.
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ISO 16844-3:2004(E)

R3 = 10 kΩ; R4 = 330 Ω; C3 = C4 = 2,2 nF
Figure 3 — Interface data signal — Example
5.2.3 Voltage monitoring and watchdog signal
5.2.3.1 Electrical requirements
The electrical requirements of the voltage monitoring of supply voltage over poles 1 and 2, and the watchdog
signal, both submitted via pole 4, shall be in accordance with Table 3.
Table 3 — Requirements of the watchdog signal voltage monitor
Electrical
requirements
Parameter Remark
Min. Typical Max.
5,0 V — U If the supply voltage is below 6,5 V, the sensor may not reply to any
pos sply
a
Voltage monitor
request, but if it is below 5,0 V, it does not reply.
6,5 V
t — — 1 s Sensor watchdog reset delay time
don
t — — 1 s Sensor watchdog recover time
doff
Watchdog
b
signal
t
1 s — — Watchdog on time
won
t 1 s — — Watchdog off time
woff
a
See block diagram of data signal in Figure 3.
b
See data signal (in) U , see 5.2.3.2.
low

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ISO 16844-3:2004(E)
5.2.3.2 Timing diagram watchdog signal
If the vehicle unit discovers a time-out of an expected response, it shall be possible to start another attempt or
send a watchdog signal to the motion sensor in accordance with Figure 4 and, for voltage levels and timing, in
accordance with Table 3. If the motion sensor detects a watchdog signal at pin 4, it shall restart its program
(see 7.5.3)
The reset shall not effect the speed real time signal of pin 3.


Key
1 normal data signal
2 tachograph sends watchdog signal
3 requirement
4 watchdog detection
5 example
Figure 4 — Timing of watchdog signal
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ISO 16844-3:2004(E)
5.2.4 Block diagram of the speed signal, real time
The speed signal, real time is a digital signal with a frequency proportional to the rotary speed of the scanned
impulse wheel. Manipulations of this signal shall be of no effect to the messages. Resistance R2 of Figure 5
limits the input current, so it is responsible for overload and short circuit protection.

R1 = 4,7 kΩ; R2 = 1,5 kΩ; C1 = C2 = 1 nF
Figure 5 — Speed signal, real time — Example
6 Cable
The cable for connecting the motion sensor to the vehicle unit shall provide distributed core capacitances of
CS < 2,0 nF. The cable impedances depend on parasitic capacitances, inductances, resistances, etc., which
influence the transfer characteristic of the cable. The parasitic capacitances (see Figure 6) are of the greatest
influence for the frequency range.

Figure 6 — Equivalent circuit of the cable parasitic capacitances
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ISO 16844-3:2004(E)
7 Interface protocol
7.1 Transmission
7.1.1 Data rate and structure of data frame
The transfer of data shall be serial and asynchronous with a baud rate of 1 200 Baud.
The structure of one byte shall be according to Figure 7: 1 start bit, 8 data bits, 1 parity bit (even) and 1 stop
bit
Start D0 D1 D2 D3 D4 D5 D6 D7 Parity Stop
Start bit shall be low state.
Stop bit shall be high state.
Figure 7 — Structure of one data frame message structure
7.1.1.1 Request from vehicle unit to motion sensor
The message structure of a request from the vehicle unit to the motion sensor shall be according to Figure 8.
Header Data bytes Tail
Instruction Data
Sync Target STX Length ETX LRC
No. (depending on the instruction number)
LRC = XOR from Sync to ETX
Figure 8 — Structure of the requests
7.1.1.2 Acknowledge from motion sensor to vehicle unit
The acknowledge from the motion sensor shall be sent as 1 byte, with the instruction number appropriate to
the vehicle unit, if a correct request was detected.
7.1.1.3 Break from the vehicle unit
If the vehicle unit receives an incorrect acknowledge from the motion sensor, the vehicle unit may send a
break byte as shown in Figure 9.
If the motion sensor detects a break byte, the scheduled reply shall be aborted and the motion sensor shall be
ready for a new request. See also 7.1.2.
Value don’t care
Figure 9 — Structure of break

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ISO 16844-3:2004(E)
7.1.1.4 Reply from the motion sensor to the vehicle unit
The motion sensor shall send the message according to Figure 10 if data have been requested from the
vehicle unit.
Header Data bytes Tail
Sync Target STX Length Data ETX LRC
LRC = XOR from Sync to ETX
Figure 10 — Structure of reply
7.1.1.5 Sync byte
The sync byte shall be a byte of the value 192 decimal, used for controlling the baud rate.
7.1.1.6 Target byte
The target byte shall identify the direction of transmission, where
 logic “0” identifies transmission direction from the vehicle unit to the motion sensor, and
 logic “1” the direction from the motion sensor to the vehicle unit.
7.1.1.7 STX byte
The STX byte shall be a constant byte of the value 2 decimal.
7.1.1.8 Length byte
The length byte specifies the length of the complete message from the sync byte to the LRC; the LRC byte is
included.
7.1.1.9 Data bytes
The data bytes shall contain information interchanged between motion sensor and vehicle unit.
7.1.1.10 ETX byte
The ETX byte shall be a constant byte of the value 3 decimal.
7.1.1.11 LRC byte
The LRC byte shall be an arithmetical XOR from Sync until ETX, including ETX.
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ISO 16844-3:2004(E)
7.1.1.12 Timing
During normal operation, the timing parameters shall be those according to Figure 11, which shall be in
accordance with Table 4.

Figure 11 — Structure of timing during normal operation
Table 4 —Timing values
Value
Timing Description
min. max.
ms ms
P1 0 10 Inter byte timing for external request
P2 0 25 Timing between the external request and the acknowledge from motion sensor
P3 0 10 Timing in which the break of an acknowledged request is possible
P4 10 30 Timing between the acknowledge and the motion sensor response
P5 0 10 Inter byte timing for motion sensor response
a
Timing between the motion sensor responses and start of a new external request
P6 30 to 25 200 —
a
Min. and max. timing of period P6 depend on the instruction number.

7.1.2 State diagram — Communication and execution of instructions
Figure 12 shows the execution of the programs within the motion sensor and the vehicle unit and how it is
affected by the communication.
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ISO 16844-3:2004(E)

Figure 12 — State diagram of communication and execution of instructions

7.2 Motion sensor state at the end of production
The motion sensor shall be prepared for pairing when it leaves the factory, i.e. the following values shall be
stored in its non-volatile memory:
 the extended serial-number of the motion sensor in plain text, N , see 7.6.9.6;
S
e
 the extended serial-number of the motion sensor encrypted with the identification key, K (N );
ID S
 the pairing key of the motion sensor in plain text, K
P;
 the pairing key of the motion sensor encrypted with master key, e (K ).
K P
The master key and identification key shall not be stored in the non-volatile memory of the motion sensor. The
pairing key shall be unique to each motion sensor. The pairing key is only used to pair the motion sensor and
the vehicle unit. The two 64 bit halves of the pairing key are distinct. A unique session key is generated during
the pairing. The session key is different from the pairing key.
The master key shall not be stored completely within the vehicle unit memory. The identification key shall not
be stored within the vehicle unit memory and shall be derived by adding a constant control vector of the value
48 21 5F 00 03 41 32 8A || 00 68 4D 00 CB 21 70 1D hexadecimal on the master key (K =K XOR CV).
l
ID
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ISO 16844-3:2004(E)
The following information shall also be stored in the non-volatile memory of the motion sensor when it is
shipped:
 motion sensor type in plain text;
 date of production of the motion sensor in plain text;
 operating system identifier of the motion sensor in plain text;
 security identifier of the motion sensor (type of processor used) in plain text;
 type approval number of the motion sensor in plain text;
 name of the motion sensor manufacturer in plain text.
7.3 Instructions
Instructions numbers shall be in accordance with Table 5.
Table 5 — Instruction numbers
Motion sensor Timing to
Vehicle unit
next
request
Reply
Instruction-
instruction
number
Header Instruction Data Tail Acknowledge Header Instruction Data Tail
ms
Bytes Bytes Bytes Bytes bytes Bytes Bytes Bytes Bytes
12 600 to
21 000
b
a a a a
10 4 1 8 2 1 depending

on the file
d
number
e
11 4 1 0 2 1 4 0 2 30


c
40 4 1 0 2 1 4 0 2 30
8
b b
41 4 1 8 2 1 4 0 16 2 30
b
a a a a
42 4 1 16 2 1 8 400

b
a a a a
43 4 1 2 1 25 200
24

b
50 4 1 0 2 1 4 0 2 200
24
b
a a a a
70 4 1 8 2 1 8 400

b
80 4 1 0 2 1 4 0 8 2 30
a
There will no response to the request except the acknowledge.
b
The data bytes of the concerned instruction will be transmitted encrypted.
c
The data bytes shall not be encrypted.
d
See Table 9.
e
See Tables 10 and 11.
7.4 Initialization of communication between motion sensor and vehicle unit
7.4.1 General
The motion sensor shall be matched with the vehicle unit by the interchange of pairing data.
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ISO 16844-3:2004(E)
7.4.2 Necessary sequence of instruction for pairing
7.4.2.1 Overview
Table 6 details the sequence of instruction numbers necessary for pairing.
Table 6 — Sequence of instructions for pairing
Vehicle Direction of data Motion
Remark
unit transfer sensor
40 ΠInitializes pairing

Í Acknowledge See 7.1.2.
The motion sensor sends its serial number N .
Í Response
s
The vehicle unit sends the extended serial number of the sensor
41 Î
encrypted with identification key.
Acknowledge See 7.1.2.
Í
If the vehicle unit is authorised, the sensor returns the pairing key
Í Response
encrypted with master key.
42 The vehicle unit sends the session key, encrypted with pairing key.
Î
Í Acknowledge See 7.1.2.
The vehicle unit sends the pairing information, encrypted with pairing
43 Î
key.
Í Acknowledge See 7.1.2.
50 ΠRequest for authentication
Í Acknowledge See 7.1.2.
Response The sensor sends the pairing information encrypted with session key.
Í

7.4.3 Pairing initialization of vehicle unit and motion sensor
7.4.3.1 General
The timing between transmission of the initializing instruction and the next instruction shall be at least thirty
milliseconds (P6 = 30 ms min.).
7.4.3.2 Initialization message
The vehicle unit shall initialize the pairing by transmitting instruction No. 40 to the motion sensor (see
Figure 13).
Instruction
Sync Target STX Length ETX LRC
No.
192 0 2 7 40 3 238
Figure 13 — Structure of instruction 40 for pairing Initialization

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ISO 16844-3:2004(E)
7.4.3.3 Response from the motion sensor to the vehicle unit
The extended serial-number of the motion sensor as shown in Figure 14 shall be sent to the vehicle unit in
plain text as response to received instruction No. 40.
The content of data bytes on the data line shall be N
.
S

Sync Target STX Length Extended serial-number of motion sensor ETX LRC
192 1 2 14 Byte 0 Byte 1 Byte 2 Byte 3 Byte 4 Byte 5 Byte 6 Byte 7 3 x
Figure 14 — Structure of response to instruction 40

7.4.4 Transmission of encrypted serial number of motion sensor
7.4.4.1 General
The encrypted serial number of the motion sensor shall be transmitted from vehicle unit to motion sensor. The
timing between transmission of this instruction and the next instruction shall be at least thirty milliseconds
(P6 = 30 ms min.).
7.4.4.2 Request
The vehicle unit shall encrypt the extended serial number of the motion sensor, using the identification key
and transmit it as an eight (8) byte block to the motion sensor with instruction No. 41 as shown in Figure 15.
e
The content of data bytes on the data line shall be K (N ).
ID S
Instruction Extended serial number of motion sensor
Sync Target STX Length ETX LRC
No. encrypted with identification key
192 0 2 15 41 Byte 0 Byte 1 Byte 2 Byte 3 Byte 4 Byte 5 Byte 6 Byte 7 3 x
Figure 15 — Structure of instruction 41 — Transmission of encrypted extended serial number
of motion sensor
7.4.4.3 Response
The motion sensor then compares the received data with the stored encrypted extended serial number. If they
are equal, it is assumed that the authentication of the vehicle unit to the motion sensor is correct. In this case
the motion sensor transmits a pairing key which is encrypted with the master key to the vehicle unit. The
content of data bytes on the data line, as shown in Figure 16, shall be e (K ).
K P
Pairing key
Sync Target STX Length ETX LRC
encrypted with master key
Byte Byte Byte Byte    Byte Byte Byte Byte
192 1 2 22 3 x
0 1 2 3 . . . . . 12 13 14 15
Figure 16 — Structure of response to instruction 41 — Transmission of pairing key to the vehicle unit
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ISO 16844-3:2004(E)
7.4.5 Transmission of session key from vehicle unit to motion sensor
7.4.5.1 General
The timing between transmission of this instruction and the next instruction shall be at least eight thousand
four hundred milliseconds (P6 = 8400 ms min.).
7.4.5.2 Request
The vehicle unit checks that the two 64 bit halves of the pairing key are distinct. Then, subject to this condition,
the vehicle unit shall send the session key encrypted with the pairing key (see Figure 17) and shall transmit it
with instruction No. 42 as a sixteen (16) byte block
...