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Flying High with
STANAG 3910
A STANAG3910
Tutorial
Feb 2015
v2.02
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Notice
The information that is provided in this document is believed to be accurate. No
responsibility is assumed by AIM for its use. No license or rights are granted by implication
in connection therewith. Specifications are subject to change without notice.
© Copyright 1999-2002 : AIM
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Flying High with STANAG3910
Overview and History
As the EF2000 Typhoon enters the production stage of its development, STANAG3910, EFAbus will
get its first chance to prove itself by meeting the mission critical avionics requirements for this highly
sophisticated fighter aircraft.
Since it was established at the early stages of the programme that the data transfer capacity of the
MIL-STD-1553B bus was not going to fulfil the requirements, STANAG3910 was selected by the
Eurofighter (UK, Germany, Italy & Spain) consortium in 1989 to meet the demanding Avionics
Systems needs of such an aircraft.
Very simply STANAG3910, EFAbus is based on using the existing MIL-STD-1553B, 1Mbit/sec dual
redundant Low Speed (LS) bus augmented by a High Speed, (HS) Fibre Optics (Reflexive Star
Topology) dual redundant bus operating at 20Mbits/sec. The LS bus provides the command and
control of the HS bus by use of ‘Action Words’ sent over the LS bus. The HS bus is used only for
Data Transfers under the control of these ‘Action Words’.
The bus architecture comprises a Bus Controller (BC) with up to 31 Remote Terminals (RT’s). Each
device can have a LS/HS connection as shown in Figure 1.
Bus Concept
Bus
Controller
LS-BIU
HS-BIU
Remote
Terminal
LS-BIU
HS-BIU
Remote
Terminal
• • •
LS-BIU
Bus
Monitor
LS-BIU
HS-BIU
Dual
Redundant
LS-Bus
(Electrical)
•••
•••
F/O
Reflexive
Star Coupler
F/O
Reflexive
Star Coupler
Dual
Redundant
HS-Bus
(Optical)
In the case of the EF2000 implementation, RT Sub-address 26 (decimal) on the LS bus is reserved
as the HS Sub-address. All HS transfers are initiated via the LS bus with Command and Status
words for the HS bus being transferred as LS datawords. The transfer types are as defined in the
MIL-STD-1553B with no automatic acknowledgement of HS data transfers in the basic protocol.
Therefore HS RT status must be polled by the transmitting terminal. It will be seen that this dual bus
approach allows the mixed operation of both STANAG3910 and MIL-STD-1553B terminals.
The first draft of this dual speed MIL-STD-1553B based bus was created in Germany during 1987. In
1988, this first draft was submitted to the AVS WP in Brussels. Following this in 1989, a project
specific variant known as EFAbus was issued. This is the version used today (with some updates)
for the EF2000 aircraft project.
STANAG3910 Overview
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It should be appreciated that this standard was adopted due to the lack of a truly available off the
shelf ‘High Speed Data Bus’ for Avionics applications. This, in conjunction with the reasons listed
below, drove the down selection of the STANAG3910, EFAbus for the EF2000, Typhoon aircraft:
•
•
•
•
Allow evolution from MIL-STD-1553B bus only to ‘Higher Speed’ Avionics Bus System
Mixing of MIL-STD-1553B/ STANAG3910 Avionics Systems
‘Low Risk’ approach with first EF2000 Prototypes using MIL-STD-1553B only
Stay with a ‘Deterministic’ Master/ Slave Protocol
Physical Layer of the HS Bus
The implementation using Fibre Optic technology STANAG3910 HS bus was to eliminate Electro
Magnetic Interference (EMI) and reduce the susceptibility to lightning, radiation and Nuclear Electro
Magnetic Pulses (NEMP). The STANAG3910 standard defines the physical layer of the HS bus for
both Electrical and Fibre Optical implementations. The fibre optic topologies can be implemented in
several ways:
•
•
•
Transmisive Star
Reflexive Star (used for EF2000, Typhoon)
Linear Bus
Figure 2 shows s a Transmissive Star Coupled bus. The advantages to this topology is that you
have a favourable ‘Optical Power Budget’ with a similar Optical Input Signal level for all Terminals.
The disadvantages are that expansion is very difficult and two fibre optical cables are required (four
fibres per dual redundant Terminal).
TX
Terminal
#1
RX
TX
Terminal
#2
RX
•
•
•
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Transmissive
Star
Coupler
•••
TX
Terminal
#n
•••
RX
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Figure 3 shows a Reflexive Star Coupled bus topology. The advantages of such a topology include
a reasonable Power Budget, similar optical input power for all Terminals and a minimal fibre opticcabling requirement. The disadvantages are that expansion is very difficult and an ‘Optical Splitter’ is
required in each Terminal.
Terminal
#1
TX
RX
Splitter
Terminal
#2
TX
RX
•
•
•
Splitter
•
•
•
Terminal
#n
Reflective
Star
Coupler
TX
RX
Splitter
Figure 4 shows a Linear Tee Coupled Bus. The advantages of such a topology are that expansion
is easy. However the disadvantage is that the receiver input signal level is position dependant which
means receiver must have a wide dynamic range, hence it has a bad Optical Power Budget.
TX
Terminal
#1
Coupler
RX
TX
Terminal
#2
Coupler
Coupler
Coupler
RX
•
•
•
TX
Terminal
#n
RX
STANAG3910 Overview
Coupler
Coupler
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The Reflexive Star Optical implementation selected for the EF2000 uses the following parameters:
•
•
•
•
•
Wavelength
Transmitter Output
Receiver Sensitivy
Bit Error Rate
Fibre
770…850 nm
-0.5 +/- 3.5dbm (peak)
- 37 dbm (peak)
< 10 –10
200/280 µm, step index, numerical aperture 0.24
Transfer Protocol
Specifically the LS bus handles the transfer protocol. Once the LS Bus Controller further has
initiated an HS LS BC messages can be initiated. STANAG3910 defines several HS transfer types,
which are shown in the figures below:
LS Bus
Command
Word
HS Action
Word
TI
HS Bus
**
##
TI
:
:
:
Figure 5
LS Bus
Command
Word
:
:
Figure 6
Next
Transfer
HS Message Frame
HS BC and RT to BC Transfer
Next
Transfer
##
TI
##
TI
##
MIL-STD-1553B Response Time ( 4 ... 12 µs )
MIL-STD-1553B Intermessage Gap ( > 4 µs )
HS Transmitter Initialise Time (24 ... 32 µs )
HS Action
Word
HS Bus
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Status
Word
**
HS Message Frame
MIL-STD-1553B Intermessage Gap ( > 4 µs )
HS Transmitter Initialise Time ( 24 ... 32 µs )
HS BC Broadcast Transfer
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LS Bus
Command
Word
HS Action
Word (RX)
**
Status
Word
##
Command
Word
HS Action
Word (TX)
**
HS Bus
Status
Word
##
TI
RI/RIOUT
**
##
TI
:
:
:
Command
Word
HS Action
Word (RX)
HS RT to RT
##
Command
Word
HS Action
Word (TX)
**
Status
Word
TI
HS Bus
RI/RIOUT
Figure 8
HS Message
Frame
MIL-STD-1553B Response Time ( 4 ... 12 µs )
MIL-STD-1553B Intermessage Gap ( > 4 µs )
HS Transmitter Initialise Time (24 ... 32 µs )
Figure 7
LS Bus
Next
Transfer
##
Next
Transfer
HS Message
Frame
HS RT Broadcast
HS Mode Code transfers use the BC to RT or BC Broadcast transfer of one action word and
optionally one data word. At this point in time the standard does not define HS Mode Codes with an
additional data word. The Mode Codes currently defined are as follows:
Hex Value
HS Mode Code
03
04
05
08
09
OA
Initiate HS Self Test
HS Transmitter Shutdown
Override HS Transmitter Shutdown
Reset HS Terminal
HS Receiver Initialise
HS Transmitter Initialise
To perform an HS Status check a RT to BC transfer has to be issued via the LS bus. The Word
Count maybe variable but no transactions take place on the HS bus. The HS Status Word is in the
first data word, HS Action Word in the second word and the HS Built in Test (BIT) in the third word.
With regards with BIT word, STANAG3910 EFAbus does not define the usage of these bits.
STANAG3910 Overview
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Figure 9 shows the HS Status Check sequence sent on the LS bus.
Command
Word
Status
Word
**
HS Status
Word
Last HS
Action Word
HS BIT
Word
Data
Word 1
Data
Word 1
••
Both the LS and HS buses have strict Protocol timing requirements defined. In the case of the LS
bus this is the same as STANA3838 (equivalent to MIL-STD-1553B). For the HS bus the following
protocol timing requirements are defined:
Transmitter Initialise Time
Receiver Initialise Time
Receiver Initialise Timeout
Data Streaming Timeout
Inter Transmission Gap
24…32µs
24µs max.
185 +/- 15µs
4.15 ms +/- 20%
2µs
HS Action Word
The HS Action Word is a data word sent by the BC to HS Sub-Address of one or all Terminals on
the LS bus. It controls any HS data transfer and contains any HS Mode Code specification as
required by the BC. The HS action word is always a ‘One Word Message’ on the LS bus generated
by the BC. The HS Action words for Data Transfers and Mode Codes are shown in Figures 10 &
11.
MSB
15
14
HS A/B
HS T/R
13
LSB
0
7 6
HS Message Identify
HS Block Count
Figure 10
•
HS A/B:
HS Bus Select
0:
1:
use HS Bus A
use HS Bus B
•
HS T/R:
HS Transfer Direction
0:
1:
Receive
Transmit
•
HS Message Identify:
7 Bit HS 'Subaddress'
•
HS Block Count:
Number 32 Word blocks contained in HS Message Frame
MSB
15
HS A/B
14
HS T/R
13
7
0 0 0 0 0 0 0
LSB
0
6
HS Mode Code
Figure 11
•
HS A/B:
HS Bus Select
0:
1:
use HS Bus A
use HS Bus B
•
HS T/R:
HS Transfer Direction
0:
1:
Receive
Transmit
•
HS Mode Code :
- 6 HS Mode Codes are defined, for all of them Broadcast is allowed
- 9 Mode Codes are reserved
- 2 reserved Mode Codes with Data Word
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HS Status Word
The HS Status Word definition is shown in Figure 12 below.
MSB
15
14
HS TF
HS Receiver Status HS Transmitter Status
9 8
LSB
0
3 2
Reserved
Figure 12
•
HS TF:
HS Terminal Flag ( optional )
•
HS RX Status
Bit 14 : HS Message Frame Error
Bit 13 : HS Receiver Active
Bit 12 : HS Receiver not ready ( optional)
Bits 9...11:
reserved (set to 0)
•
HS TX Status
Bit 3 : HS Transmitter active
Bit 4: HS Transmitter not readies (optional)
Bits 5...8:
reserved (set to 0)
HS Message Frame
The HS Message Frame contains several elements, which are common with the SAE HS Bus
Standard. The HS frame length is a minimum of 624 bits up to a maximum of 65,648 bits depending
on the type of HS message transfer, which takes place. It contains a Preamble, Start Delimiter,
Headers, Word Count, Information field, Error Detection (CRC) and an End Delimiter.
Figure 13 below shows the make up of the HS Message Frame
Preamble
SD
FC
PA
DA
WC INFO
CRC
ED
Figure 13
The following describes the elements, which make up the HS Message Frame
Preamble -
This is 40 bits of Manchester Encoded logic ‘1’s (20Mhz square wave signal)
and is used for gain control of the receivers, receiver clock recovery and the
decoding of the Start of Frame.
Start Delimiter -
This is 8 bits of Manchester Code Violations and contains a unique pattern to
identify the start of HS frame.
Bit 0
Bit 1
Bit 2
Bit 3
ON
OFF
STANAG3910 Overview
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Headers -
Header information is contained within 3 x 16 bits.
The FC/PA comprises a 1 x 16 bit Manchester Encoded Word. The Frame
Control (FC) is an 8 bit field set to a pattern of ‘1100 0000’. The Physical
Address (PA) is an 8 bit field and specify the RT Address of the transmitting
terminal (for BC=31).
The Destination Address (DA) is a 1 x 16-bit word. If the MSB is set to ‘0’
Physical Addressing is used. If the MSB is set to ‘1’ Logical Addressing is
used. For the EF2000 Logical Addressing is used.
The Word Count Field (WC) is a 1 x 16-bit word and defines the number of
words contained in the Information Field.
Information Field -
The Information Field contains between 32 and 4096 words, each being 16
bits. The number of words is always a multiple of 32.
CRC -
The HS Message contains a CRC check word, which covers all the words
between the Start and End Delimiter fields. The general Polynomial, which is
used for STANG3910, is in accordance with the CRC-CCIT standard
Polynomial:
G (x) = x16+x12+x5+1
On the receiving side the CRC generating process is repeated and the received checkword is
compared with the generated checkword. Using this approach the BC or RT has a way to validate
the HS data.
End Delimiter -
This is 4 bits of Manchester Code Violations and contains a unique pattern to
identify the end of the HS frame.
Bit 0
Bit 1
Bit 2
Bit 3
ON
OFF
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STANAG3910 Test & Validation
A number of Test and Validation Test Plans documents have been created by the EF2000, Avionics
Joint Team (AJT). These have been created for the suppliers of STANAG3910 Avionics equipment
and components to the EF2000 project to be sure designs and production units conform to the
EFAbus standards. These Test Plans have been created to define, as a minimum, what Protocol
and Optical test must be performed before delivering Avionics equipment’s for use on the EF2000 or
the aircraft rigs prior to flight.
Test Plans include:
•
•
EFAbus RT and BC Production Test Plan
EFAbus RT and BC Validation Test Plan
• Validation Test is a ‘Super Set’ of the Production Test Plan
• Includes Optical and Protocol Tests
• STANAG3838 Test Plans (MIL-HDBK-1553 and SAE AS4113 form part of the EFAbus Test
Plans)
Databus Analyser and Modules for STANAG3910 Test & Simulation
As with the MIL-STD-1553B avionics databus, it was recognised by company AIM GmbH that
Databus Analyser equipments and modules would be a requirement for the development, simulation
and production equipment’s for the EF2000 project. With this in mind, AIM GmbH produced the
worlds first commercially available ‘STANAG3910 VMEbus card’ and ‘Demonstrator System’ in 1989
for potential STANAG3910 Avionics users. Two such systems where supplied to CASA, British
Aerospace for evaluation and test at the conceptual stages of the project.
The Test and Validation requirements of the Protocol and Optical requirements of the STANAG3910
standard proved to be a big challenge. AIM GmbH rose to this challenge and created a
STANAG3910 Fibre Optics and Protocol Test System (CTX) which allowed users to test
STANAG3910 equipments against the EFAbus Validation and Production Test plans.
This led to the creation of a Databus Analyser system known commercially as the ‘MBA-90’
(Modular Bus Analyser). Built using VMEbus cards and controlled via a host PC, the MBA-90
STANAG3910 Databus Analyser soon became the ‘Defacto Standard’ across the entire EF2000
project. Today, AIM GmbH enjoy the enviable position as the leading supplier to three of the EF2000
Prime Contractors and major Sub-Contractors in the UK, Germany, Italy and Spain for all Databus
Analysers, VMEbus, VXIbus and PCI based Test & Simulation Modules. This has been no easy
task. Much hard work, dedication and private company funding has been put in by the AIM GmbH
team to support STANAG3910 to make
STANAG3910 Overview
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