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 CablesSerial interface modulesTerminal 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 field3. A single parity bit4. 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. Synchronization gap (SG) timer

3. 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. It begins the moment the terminal starts to transmit.2. All LRUs have same TI.

• Synchronization Gap ( GP )1. The SG begins when there is no signal on the bus.2. The SG is the same for all LRUs.3. It has a value larger than the value of the longest TG used on a given bus.4. If a signal comes on the bus before SG completes , the SG stops.5. When SG completes it stays reset until the LRU transmits again.

• Terminal GAP (TG )1. Each LRU has same a special TG.2. The TG begins after the SG is complete and no signal is on the bus.3. If there is a signal on the bus before the TG completes ,the TG stops.4. It starts again when there is no signal on the bus.5. The TG and SG cannot overlap in time. 6. They must occur in sequence.

COMPARISIONParameter 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 No Yes

Application B 737 NG B777