This document discusses digital avionics architecture and various avionics data buses. It covers the evolution of avionics architectures from early disjoint and centralized systems to modern distributed architectures like Pave Pace. Key data bus standards are described including MIL-STD-1553B, ARINC 429, 629, and AFDX. Electrical and optical data bus systems are compared, and limitations of electrical buses discussed. Integrated modular avionics and use of commercial off-the-shelf components is also summarized.

1. AE8751 - AVIONICS
Dr. K. Kannan, M.E., M.E., Ph.D.,
Associate Professor & Head,
Department of Mechatronics Engineering
UNIT II
DIGITAL AVIONIC ARCHITECTURE (9)

2. OBJECTIVES
• To introduce the basic of avionics and its need
for civil and military aircrafts
• To impart knowledge about the avionic
architecture and various avionics data buses
• To gain more knowledge on various avionics
subsystems

3. UNIT II
DIGITALAVIONIC ARCHITECTURE (9)
• Avionics system architecture
– Data buses
– MIL-STD-1553B
– ARINC – 429
– ARINC – 629.
• CO2: To impart knowledge about the avionic
architecture and various avionics data buses

4. AVIONIC ARCHITECTURE
The term avionics architecture is a simple
description for a very complex and multi-
faceted subject.
An avionic architecture is the total set of design
choices which make up the avionic system and
result in performing as a recognizable system.
In effect, the architecture is the total avionics
system design.

5. EVOLUTION OF AVIONICS ARCHITECTURE
First Generation Architecture (1940’s –1950’s)
Disjoint/Independent Architecture
Centralized Architecture
Second Generation Architecture (1960’s –1970’s)
Federated Architecture
Distributed Architecture
Hierarchical Architecture
Third Generation Architecture (1980’s –1990’s)
Pave Pillar Architecture
Fourth Generation Architecture (Past 2005)
Pave Pace Architecture

6. First Generation
DISJOINT ARCHITECTURE

7. First Generation
DISJOINT ARCHITECTURE

8. First Generation
CENTRALIZED ARCHITECTURE

9. First Generation
CENTRALIZED ARCHITECTURE

10. Second Generation
FEDERATED ARCHITECTURE
In this Architecture, each system acts independently but
united (Loosely Coupled).
Data conversion occurs at the system level and the data
are send as digital form – called Digital Avionics
Information Systems (DAIS)
Several standard data processors are used to perform a
variety of Low – Bandwidth functions such as
navigation, weapon delivery, stores management and
flight control.
Systems are connected in a Time – Shared Multiplex
Highway.
Resource sharing occurs at the last link in the information
chain – via controls and displays.

11. Second Generation
FEDERATED ARCHITECTURE

12. Second Generation
DISTRIBUTED ARCHITECTURE

13. Second Generation
HIERARCHICAL ARCHITECTURE

14. Third Generation Architecture
PAVE PILLAR
Pave Pillar is a US Air Force program to define the
requirements and avionics architecture for fighter aircraft.
-Increased Information Fusion
-Standardization for maintenance simplification
-Provides capability for rapid flow of data from the
system as well as between and within the system
-Higher levels of avionics integration and resource
sharing of sensor and computational capabilities
-Pilot plays the role of a weapon system manager.
-Able to sustain operations with minimal support, fly
successful mission day and night in any type of weather
-Face a numerically and technologically advanced
enemy aircraft and defensive systems.

15. Third Generation Architecture
PAVE PILLAR

16. Fourth Generation Architecture
- PAVE PACE
• US Air Force initiated a study project to cut down the
cost of sensors used in the fighter aircraft.
• In 1990, Wright Laboratory – McDonnell Aircraft,
Boeing Aircraft Company and Lockheed launched the
Pave Pace Program and Come with the Concept of
Integrated Sensor System (ISS).
• Pave Pace takes Pave Pillar as a base line standard.
The integration concept extends to the skin of the
aircraft
• Integration of the sensors and this architecture was
originally designed for Joint Strike Fighter (JSF)

17. Fourth Generation Architecture
- PAVE PACE

18. Integrated Modular Architecture
A real time Computer Network Airborne system
(modular architecture) consisting of various
computing modules, with different criticality levels
Features are
1. A Dedicated Avionic System
2. Full Cockpit Control and Display System
3. Acoustic Warnings and tones to Crew
4. Autonomous Navigation system’
5. Full Plant Management feature
6. Monitoring and Diagnostic features.

19. Hierarchy of Levels
Functional allocation level:
The arrangement of the major system components and the allocation
of system functions to those components.
Communications level:
The arrangement of internal and external data pathways and data
rates, transmission formats, protocols and latencies.
Data processing level:
Central or distributed processing, processor types, software
languages, documentation and CASE (computer aided software
engineering) design tools.
Sensor level:
Sensor types, location of sensor processing, extent to which
combining of sensor outputs is performed.
Physical level:
Racking, box or module outline dimensions, cooling provisions,
power supplies.

20. Software Architecture

21. Civil
Integrated Modular Avionic Systems
As in military systems, the use of new hardware, software and
communication technologies has enabled the design of new
system architectures based on resource sharing between
different systems.
Current microprocessors are able to provide computing
capabilities that exceed the needs of single avionics
functions. Specific hardware resources, coupled with the
use of Operating Systems with a standardised Application
Programming Interface provide the means to host
independent applications on the same computing resource in
a segregated environment.
The AFDX Communication Network provides high data
throughput coupled with low latencies to multiple end users
across the bus network.

22. Civil
Integrated Modular Avionic Systems

23. Integrated Modular Avionic Systems on A380

24. Military Integrated Avionic Systems Architecture

25. Commercial Off-the-Shelf (COTS)
COTS refers to the use of commercially available electronic
hardware and/or software for the implementation of avionics
systems. This hardware and software is designed for the
general electronics marketplace, especially in the industrial
control and personal and industrial computing sectors.
Until the mid-1990s, the majority of avionic systems were
specifically designed for the application, although these used
commercial components where suitable parts were available.
The use of complex electronic systems in the automotive sector is
a growth area that mirrors some of the environmental
constraints required by avionic systems, although to date, such
systems have not employed COTS technology

26. COTS systems and equipment are being used in commercial
and military transport aircraft where the operating
environment is relatively benign. This is initially found in
areas where there is minimal risk from the failure of the
systems, e.g. cabin entertainment systems, communications
and long-term navigation, and includes both hardware and
software.
The application of COTS equipment to military fighter and
strike aircraft is limited due to all aspects of the operating
environment; mechanical (vibration, shock), climatic
(temperature and pressure) and electromagnetic (including
lightning and radiation effects). Special ‘ruggedised’
hardware is available at a significant cost premium.
Commercial Off-the-Shelf (COTS)

27. The use of COTS hardware and software equipment for
applications that are safety-critical, e.g. flight and
propulsion control sub-systems, raises issues
associated with the certification of such systems.
Certification imposes demonstration of fitness for
purpose, and assessments that all reasonable actions
have been taken to ensure that the risk of failure is at
an acceptably low level.
Commercial Off-the-Shelf (COTS)

28. Experience has shown that there are significant and
possibly unacceptable risks with the use of COTS,
both hardware and software, because of:
• Lack of design quality, documentation,
guarantees and warranty.
• Lack of stable standards and specifications.
• Short lifetime dictated by commercial
pressures.
• Lack of guaranteed forward and backward
compatibility
Commercial Off-the-Shelf (COTS)

29. Data Bus Systems

30. Data Bus Systems
• Data bus systems are the essential enabling
technologies of avionic systems integration in both
federated and integrated modular avionics architectures.
• They can be broadly divided into
– Electrical data bus systems where the data are transmitted
as electrical pulses by wires
– Optical data bus systems where the data are transmitted as
light pulses by optical fibres.
– Serial digital data buses are used for interconnecting sub-
units and sub-systems whereas Parallel data buses are used
within a unit or rack for interconnecting the individual
modules.

31. Electrical Data Bus Systems
The electrical serial digital data bus systems used
in avionics systems are divided into two
categories in terms of their data rate
transmission capabilities.
- low data bus systems operating with a
maximum throughput of 1 to 2 Mbits/s
- high speed data bus systems with a
throughput of 50 Mbits/s to 100 Mbits/s.

32. Low data bus systems
This system is very widely used in military aircraft worldwide,
although it originated in the US since 1975 and used in MIL
STD 1553 B . It transmits and receives data at 1 Mbit/s.
An understanding of its operation extends to the other systems in
many areas, such as ARINC 429 which is a point to point
system of lower capabilities (10 Kbits/s data rate) used in civil
avionic systems and the more recent ARINC 629 data bus
system.
The ARINC 629 data bus system is similar to MIL STD 1553 B
system. The difference is ARINC 629 is an autonomous
system, whereas the ‘1553’ system is a ‘command response’
system operated through a Bus Controller.
The ARINC 629 data bus system which is installed in the Boeing
777 airliner operates at 2 Mbits/s as opposed to 1 Mbits/s for
‘1553’ data bus system.

33. High speed data buses
There are two standard high speed data buses which have
been developed in the US for military applications.
These are the ‘Linear Token Passing Bus’, LTPB, which
operates at 50 Mbits/s and the ‘High Speed Ring Bus’,
HSRB, which operates at 100 Mbits/s.
The high speed data bus system which is adopted in new
civil aircraft is a system based on the ‘Ethernet’ data
bus. The Ethernet data bus system is used in
commercial computing system applications. It has a
data rate transmission capability of 100 Mbits/s and is
mainly used for data file transfer.

34. Multiplex data bus system architecture

35. Limitations of Electrical Data Bus Systems
Relatively slow transmission rate limited by medium
(1 Mbit/s)
Restricted number of terminals for communication
(max 31)
Restricted number of words transferred per message
(max 32)
Central control unit managing all data transfer.

36. Optical Data Bus Systems
The transmission of light signals along any
optical fibre depends on the optical property of
total internal reflection.

37. Multi-Mode Optical Fibre

38. Pulse broadening

39. Single Mode Optical Fibre
This pulse dispersion is unacceptable for
telecommunications applications which require
very high data rates and long distances between
repeaters to minimise the number of repeaters.
This resulted in the development of highly
efficient single mode optical fibres.
The major difference between single mode fibre and
multi-mode fibre is that the core diameter of
single mode fibre is of the same order of
magnitude as the wavelength of the light source.

40. Waveguide Parameter
As the core diameter is decreased and the
refractive index difference between the core
and the cladding reduced, the number of
possible guided modes for transmitting light
along the fibre decreases. There is a
normalised parameter known as the waveguide
parameter which is equal to

41. When the waveguide parameter is less than the
critical value (2.4048), then only one guided
mode is possible for transmitting light along
the fibre, and the fibre is known as a single
mode fibre.
Practical single mode fibres have ∆ varying from
0.002 to 0.005 and typical core diameters in
the range 5 to 10 µm. Typical operating
wavelength is around 1.5 µm.
Single Mode Optical Fibre

42. Material and Waveguide dispersion
There are other sources of dispersion, namely material
dispersion and waveguide dispersion which must be
minimised in order to achieve very high data rates and
very long transmission distances.
Material dispersion is the dispersion resulting from the
dependence of the refractive index of the fibre material
on wavelength.
Waveguide dispersion is the dispersion resulting from the
spectral width of the source; the different wavelength
components experience different refractive indices.
These effects can be minimised by techniques such as
grading the refractive index profile across the core.

43. Multi-mode optical fibre can be used in avionic
system applications due to relatively short lengths
involved and the current data rate requirements of
50 Mbits/s.
The reason is due to the need for demountable
connectors in avionic equipment for ease of
servicing and replacement of a failed unit. While
demountable connectors for single mode fibres
are feasible, they present a number of mechanical
alignment problems and have not progressed
beyond the laboratory stage.
Multi-Mode Optical Fibre

44. Multi-mode fibres have a considerably larger numerical
aperture than single mode fibres. The numerical aperture,
defines the semi-angle of the cone within which the fibre
will accept light and is a measure of the light gathering
power of the fibre.
NA = n1(2∆)1/2
Typical values for a multi-mode fibre are n1 = 1.46 and ∆ =
0.01 giving a NA of 0.2.
The fibre will accept light incident over a cone with a semi-
angle of sin−1 0.2, that is 11.5◦ about the axis.
Typical NAs for single mode fibres result in acceptance semi-
angles in the region of 4◦ to 8◦ as ∆ is in the region of 0.002
to 0.005. The larger NA eases the alignment tolerances of
the two halves of the connector.
Multi-Mode Optical Fibre

45. LEDs can be used for the modulated light source.
These approach a Lambertian source with a
hemispherical power profile which together with
the reasonable NA of multi-mode fibre enables a
simple and efficient optical coupling arrangement
to couple the light source to the fibre to be
implemented.
The larger core diameter eases the mechanical
tolerancing problems in aligning the two halves of
the connector.
Multi-Mode Optical Fibre

46. Major Advantages
• High data rate capability (>10 Gbit/s using
single mode fibre)
• Insensitivity to electro-magnetic interference
• Electrical isolation
• No line capacitance or mutual coupling
• Low cross-talk
• Lower power dissipation
• Reduced weight and volume requirements

47. STANAG 3910 Data Bus System
STANAG 3910 is a European data bus with a
20 Mbit/s data rate which has been adopted for the
Eurofighter Typhoon.
The bus provides an evolutionary increase in capability by
using MIL STD 1553B (STANAG 3838) as the
controlling protocol for high speed (20 Mbit/s) message
transfer over a fibre optic network.
The optical star coupler is a passive optical coupler which
enables light signals from each fibre stub to be coupled
into the other fibre stubs and thence to the subsystems.

48. STANAG 3910 Data Bus System

49. Linear Token Passing High Speed
Data Bus
The linear token passing high speed data bus
(HSDB) has been developed in the USA for
the new generation modular avionic systems
The system uses distributed control by means of
a token passing protocol and operates at
50 Mbits/s.

50. AFDX Communication Network
The new generation of civil airliners (e.g., Airbus A380),
exploit modular avionic architectures and use a
communication network adapted from the widely
commercially used Full Duplex Switched Ethernet
(FDX).
Additional features have been incorporated to meet
avionic system requirements and it is referred to as the
‘Avionics Full Duplex Switched Ethernet’, or AFDX
network.
The network provides 100 Mbits/s full duplex (two way)
communication and provides flexibility to manage any
change in the data communication between the
connected systems without wiring modifications.

51. AFDX Communication Network

52. Switched Ethernet

53. Features of Transmission Systems

54. Parallel Data Buses
Parallel data buses are used within the units or racks of the
avionic systems. These are almost invariably electrical at
the present time and use a variety of standards.
Before the availability of complex microprocessor devices, a
processor could require a complete circuit module, with the
memory devices being located on separate modules, the bus
merely being an extension of the processor signals, suitably
buffered.
As microprocessor and high-density memory devices became
available, and the functionality implemented in the systems
grew, bus technology was developed to provide inter-
processor communication with common interfaces.
In future, with a greater level of integration and the use of
commercial off-theshelf modules, there will be increased
standardisation in the parallel buses. The use of an optical
backplane for interconnecting modules is a possible future
development.

55. AVIONIC Buses

56. AVIONIC Buses
In computer architecture, a bus is a
communication system that transfers data
between components inside a computer, or
between computers.

57. AVIONIC Buses
Data Bus provides a medium for the exchange of
data and information between various Avionics
subsystems. It is used to integrate various
subsystems of Avionics in Civil and Military
aircraft systems.
Protocols are set of formal rules and conventions
governing the control of interaction among the
integrated systems.
Low level protocols define the electrical & Physical
standards whereas high level protocols deal with
data formatting.

58. Once the equipments are standardized,
equipments are easily Available, Maintainable,
reinstalled and reconfigured
(Interchangeability)
Standardization of equipments are based on the
document Military Standard (MIL-STD) and
Aeronautical Radio Inc. (ARINC)
specifications and Reports
AVIONIC Buses

59. Common types of Serial Digital Data
Transmission
Single source-single sink
Single source-multiple sink
Multiple source-multiple sink
AVIONIC Buses

60. SINGLE SOURCE-SINGLE SINK
Earliest application
Comprises a dedicated link from one piece of
equipment to another
Developed in the 1970s for use on Tornado and
Sea Harrier avionics systems

61. SINGLE SOURCE-MULTIPLE SINK
One transmitting source transmits data to a
number of recipient pieces of equipment
(sinks)
ARINC 429 is an example of this data bus which
is widely used by civil transport and business
jets.

62. MULTIPLE SOURCE-MULTIPLE SINK
Multiple transmitting sources transmits data to
multiple receivers.
This is known as a full-duplex system and is
widely employed by military users
Examples are MIL-STD-1553B and ARINC 629.

63. MAJOR DIGITAL DATA BUSES
• ARINC 429
• ARINC 629
• MIL STD 1553

64. Line Codes

65. ARINC
ARINC (Aeronautical Radio Incorporated) is a
nonprofit organization in the USA which is run
by the civil airliners with industry and
establishment representation.
It defines systems and equipment specifications
in terms of functional requirements,
performance and accuracy, input and output
interfaces, environmental requirements,
physical dimensions and electrical interfaces.

66. ARINC is a one way system where a bus is
driven by single transmitter. The bus can have
up to 20 transmitter. There is no physical
addressing. But the data are sent with proper
identifier or label.
It is a Point to Point Protocol System. It has
direct coupling of transmitter and receiving
terminals. The wire that connects transmitter
and receiver may be UTP or STP.
ARINC 429

67. ARINC 429
• It is a specification that defines a local area
network for transfer of digital data between
avionics system elements in civil aircraft.
• ARINC 429 is viewed as a permanent as a
broadcast or multicast operation
• Two ranges of transmission rates are defined
-High Speed at 100 kbps ±1%
-Low Speed in the range 12 to 14.5 kbps

68. In a differential system, information is
transmitted on two wires and one is the inverse
of the other. For ARINC 429, the voltage
measured in one wire goes from zero to +5V
and other goes from zero to -5V.
ARINC 429

69. Tx and Rx Hardware

70. ARINC 429 Bus Topology

71. ARINC 429 Star Topology

72. Tx and Rx Parameters

73. ENCODING
The signal has three states 'HIGH', 'NULL' and
'LOW' represented by the differential voltage
between the two wires of the cable.
A logical ‘1’ is signaled by transmission of a +10
±1V pulse followed by a 0±0.5V null period.
A logical ‘0’ is signaled by transmission of a –10
±1V pulse also followed by a 0 ±0.5V null
period.

74. ENCODING

75. WORD FORMAT
Label
Source/Destination Identifier (SDI)
Data field
Sign/Status Matrix (SSM)
Parity bit

76. MIL-STD-1553
Developed at Wright Patterson Air Force Base
since 1970s
Published First Version 1553A in 1975
Introduced in service on F-15 Program
Published Second version 1553B in 1978

77. SPECIFICATIONS OVERVIEW

78. ELEMENTS

79. BUS CONTROLLER
Main function is to provide data flow control for
all transmissions on the bus.
It must transmit , receive and coordinate the
transfer of information on the data bus.
All information is communicated in
command/response mode - the BC sends a
command to the RTs, which replies with a
response.

80. REMOTE TERMINAL
Device designed to interface various subsystems
with the 1553 data bus.
May be embedded within the subsystem itself, or
be an external interface to tie a non-1553
compatible device to the bus.

81. BUS MONITOR
Listens to all messages on the bus and records
selected activities
A passive device that collects data for real-time
or post capture analysis
Store all or portions of traffic on the bus,
including electrical and protocol errors
BMs are primarily used for instrumentation and
data bus testing

82. TRANSMISSION MEDIA

83. BUS ARCHITECTURE

84. TRANSMISSION METHOD
Modulation The signal shall be transferred over the
data bus in serial digital pulse code modulation
form.
Data Code Manchester II bi-phase level.
A logic one shall be transmitted as a bipolar coded
signal 1/0 (i.e., a positive pulse followed by a
negative pulse).
A logic zero shall be a bipolar coded signal 0/1 (i.e.,
a negative pulse followed by a positive pulse).
A transition through zero occurs at the midpoint of
each bit time

85. WORD FORMAT
COMMAND WORD
DATA WORD
STATUS WORD

86. COMMAND WORD

87. DATA WORD

88. STATUS WORD

89. ARINC 629
Relatively new and not widely used
Boeing Commercial Airplane Group (BCAG)
Digital Autonomous Terminal Access Communication
(DATAC) protocol
Recognized as an air transport standard by ARINC in
spec 629
Boeing 777
Source transmits either broadcast or address specific
message to all or specific receiver or sinks
If the sinks equipment needs to reply, each will need
to be fitted with own transmitter and a specific
physical bus

90. ARINC 629
BUS TOPOLOGY

91. 2 Mbps
Bipolar Manchester doublets
ARINC 629
BIT RATE & ENCODING

92. WORD FORMAT
A message has variable length and is comprised
of up to 31 word strings
Each word string has variable length and
contains
– one (20 bit) label word
– up to 256 (20 bit) data words

93. MESSAGE STRUCTURE

94. ARINC-429 VS ARINC-629

95. ARINC-429 VS ARINC-629

96. ARINC-429 VS ARINC-629

97. Data Bus Comparison

98. Thank You