ARINC - 629
DATA BUS
GENERAL
DATA BUS
• It has no shield, twisted pair of wires.
• Data speed – 2 Mbps
• bi-directional
• LRU can send data to an ARINC –629 one
at a time
• Receive data from data bus to all LRU’s at
the same time.
ARINC - 629
ARINC – 629
•
GENERAL
Many LRU’s can connect to a DATA bus in a
single communication loop.
• It is a twisted pair of wires with termination
resistors at each end.
• 120 LRUs can use one ARINC 629data bus.
• It has three parts –Data Bus Cable
- Current – Mode Couplers
-Stub Cables
Serial interface modules
Terminal controllers
ARINC-629
CHARACTERISTICS
• Many LRUs send data one at a time in
sequence.
• Many LRUs receive data at the same time.
• Communication is bi- directional.
• One LRU may connect to more than one
data bus thru separate couplers on each bus.
• All data on the bus is available to all the
LRUs on that bus.
FUNCTIONAL DESCRIPTION
• Each LRU can connect more than one
coupler to data bus.
• A current mode coupler and its terminal (TC
& SIM) move data to and from data bus.
• Only one terminal on a bus transmit at a
time.
• Wait and Watch procedure
ARINC – 629
GENERAL
CURRENT MODE COUPLER
•
PURPOSE – CONNECTION BETWEEN DATA BUS CABEL AND STUB CABLE
•
CHARACTERISTCS ---
1.
Two part assembly for fast instillation.
2.
Cover with the electronics and the receptacle for the stub cable.
3.
Base design for easy installation on panel.
4.
Waterproof housing.
5.
Protective wire guide to install the data bus
Current mode coupler
DATA BUS CABLE
• It moves data between LRUs.
• A current mode coupler and a stub cable attach
each LRU terminal to the data bus cable.
• It is pair of twisted wires with a termination
resistor at each end.
• Length – 180 feet (47.5 m) in 777.
• It connects as many as 46 current mode couplers.
STUB CABLE
• It is Bi – directional data movement between LRU and
current mode coupler.
• It also supply power from the LRUs to the current mode
coupler.
• It has four wires, two to transmit and two to receive.
• Length – 57 feet for transmit and receive couplers and 75
feet for receive only couplers
• It is in airplane wiring bundles.
STUB CABLE
ARINC – 629
Message Structure
• Data in ARINC- 629 moves as a messages.
• Between each message is terminal gap.
• A message is a group of wordstrings.
• Each wordstrings has a label word followed by data words.
• Each message has a special structure
• The structure allows the LRUs to select and read the message.
Message Structure
•
•
•
•
•
•
•
A message has 31 word strings.
There is a 4 – bit time gap between each word string.
A word string begins with label word
A word string has up to 256 data words.
There is no gap between words in word string.
Min. length – 1 label and no data words.
Max. length – 31 labels with 256 words and 30 times gaps
of 4 bits each.
Label Word Structure
•
•
A label word is a 20 – bit word.
It has :
1. A 12 - bit label field.
2. A 4 - bit label extension field
3. A single parity bit
4. A 3 - bit time hi to lo sync pulse.
A pulse of one half – bit time, called pre – sync sync pulse
(PSSP) comes before the first label word of a message.
PPSSP comes before the PSSP.
The PPSSP PSSP occur prior to 3 bit time hi lo sync pulse.
Data Word Structure
•
•
A data word is also a 20 bit word.
It has :
1. A 16 bit data field
2. A single parity bit
3. A 3 bit time lo hi sync pulse.
Timing Functional Description(General)
•
•
ARINC – 629 uses a time procedure to prevent
accidental signal mixture.
It uses three timers.
1. transmit interval ( TI ) timer
2.
3.
•
•
Synchronization gap (SG) timer
Terminal gap (TG) timer
The timers are part of LRU personality.
It is used to isolate data messages by each LRU.
Timing Functional Description
•
Time Interval (TI)
1.
2.
It begins the moment the terminal starts to transmit.
All LRUs have same TI.
•
Synchronization Gap ( GP )
1.
2.
3.
4.
5.
The SG begins when there is no signal on the bus.
The SG is the same for all LRUs.
It has a value larger than the value of the longest TG used on a given
bus.
If a signal comes on the bus before SG completes , the SG stops.
When SG completes it stays reset until the LRU transmits again.
•
Terminal GAP (TG )
1.
2.
3.
4.
5.
6.
Each LRU has same a special TG.
The TG begins after the SG is complete and no signal is on the bus.
If there is a signal on the bus before the TG completes ,the TG stops.
It starts again when there is no signal on the bus.
The TG and SG cannot overlap in time.
They must occur in sequence.
COMPARISION
Parameter
ARINC 429
ARINC 629
Direction
One way
Two way
speed
(Max.)100kbps or (Min.)12 to 14.5
kbps
2 mbps
receivers
Not more than 20
Up to 120
cable
Shielded
no shielded
components
No
Yes
structure
One label , one data field
256 labels, no.of data
field
Data transfer mode
Open loop
Communication loop
Termination of data bus
Application
No
B 737 NG
Yes
B777