5.4 - Data Buses Flashcards
What speed is the ARINC 629 data is?
2 megabits per second. Twenty times faster than ARINC 429
How many terminals can the ARINC 629 handle?
120 terminals sharing a bi directional serial data bus
What does Simplex mean in data exchange?
The transmission can flow only in one direction
What does Half Duplex mean in data exchange?
One transmitter, one receiver. The transmission can flow in both directions but only one direction at a time. (Bi-directional with limitations)
What does Full Duplex mean in data exchange?
One transmitter, one receiver. The transmission can flow in both directions at the same time (bi-directional)
What does a ARINC data bus look like?
A pair of twisted wires transmitting sets of information at periodic intervals
How does ARINC 429 check for accurate data reception
ARINC 429 prescribes the use of odd parity indication for error detection
How many transmitters and receivers are used on ARINC 429?
1 transmitter and up to 20 receivers
Can a receiver respond to a transmitter on ARINC 429
Yes, but never on the same data bus where the transmission occurred
What is the address of a LRU on the ARINC 429 network?
LRUs do not have addresses. They have equipment numbers which are grouped into equipment or system types
Advantages of serial transmission
- Only a single line is required for transmission
- Only one set of digital circuitry is needed to process the data
What are the transmission speeds of ARINC 429?
- Low Speed (LS BUS) 12-14 kbit/s
- High Speed (HS BUS) 100 kbit/s
How long are ARINC 429 words
32 bit words made of 1’s and 0’s. Separated by 4 bit times of null (zero volts)
What is BCD (Binary Coded Decimal) data used for?
Displays only, transmitted on average twice a second
What is BNR (Binary) data used for?
It’s processed by other LRUs and transmitted 6-20 times a second
What is the data word format for ARINC 429 in BNR?
1-8, 8 bit label
9-10, Source/Destination Identifier (SDI)
11-28, BNR data area
29-31, Sign/Status Matrix (SSM)
32, parity check
What is the data word format for ARINC 429 in BCD?
1-8, 8 bit label
9-10, Source/Destination Identifier (SDI)
11-29, BCD data area
30-31, Sign/Status Matrix (SSM)
32, parity check
How is the Label (Bit 1-8) transmitted
The MSB is in the LSB of the word and transmitted first on to the bus.
When is the SDI function used on the word?
When it’s necessary to indicate the source of information
What is the signal carrying the word accompanied by?
Validity and complimentary information. Covered by the SSM
What is the parity check?
It ensures the different bits forming the word have all been completely and correctly transmitted. It is used to increase transmission security
What is the maximum length of an ARINC 629 data bus?
Up to 100m long
How is the ARINC 629 data bus constructed?
Twisted pair of wires or a fibre optic cable
What are the components are included in all ARINC 629 LRUs
- Serial interface modules
- Terminal controllers
What are the characteristics of the ARINC 629 data bus system?
- LRUs send data one at a time, in sequence
- LRUs receive data at the same time
What is the serial Interface Module?
The SIM makes the transmit and the receive channel selection
What is the message structure in an ARINC 629 system?
A message has up to 31 word strings with each word string begins with a label word.
What is the time gap between each word string in an ARINC 629 system?
A four bit time gap between each word string
What is the time gap between each word string in an ARINC 629 system?
A four bit time gap
How many data words in a word string in an ARINC 629 message
256 data words with no gaps between words
What is the minimum length message of an ARINC 629 message
One label and no data words
What is the maximum length message of an ARINC 629 message
31 label words 256 data words following each label word and 30 4 bit time gaps
What are the disadvantages of the ARINC 429 point to point topology
- Each LRU needs a separate wired connection to every other LRU increasing weight.
- Whenever a new system is installed it requires new wiring to the other systems
How fast is a basic Ethernet to transmit data?
Up to 10Mbit/s
How do LRU’s connect to the Ethernet
Each LRU connects to the main backbone bus cable via stub cables
What is a key advantage of an Ethernet system?
It is a multiple access structure. Meaning any LRU can communicate with any LRU along the same bus
What does the carrier sense do?
It ensures that before any LRU transmits data, it listens to the data bus to ensue no other LRU is currently transmitting
What happens if two transmitters, transmit at the same time?
Both transmitters detect the collision and stop transmitting immediately. After a random time of listening, one transmitter will start transmitting again. This is called collision detection
How is segmentation over come in an Ethernet
Segmentation is overcome by a bridge
How does the Ethernet protocol regulate communication among nodes
Carrier Sense Multiple Access with Collision Detection (CSMA/CD)
What is a switched Ethernet?
Full Duplex
How is a switched Ethernet quicker than a basic Ethernet with CSMA/CD
The switched topology uses routers and switches. They are programmed to know which LRUs are connected
What is a Controller Area Network (CAN) bus?
It’s a multi-master broadcast serial bus standard to connect electronic control units which is an advantage over ARINC 429
What is the limit to the number of terminals on a CAN bus
There is no theoretical limit to the number of terminals, but the number is normally limited to 32 to avoid delay
How is error detection done on a CAN bus
- Monitoring data transmitted on the bus
- Cyclic redundancy check
- Message frame check
- Bit stuffing
What is AFDX
Avionic Full Duplex Switch
What are the advantages of a full duplex systems
- Data transmission is bi-directional
- Data transfer is high speed
- High data transfer rate
- Virtual link concept
- It envolves one transmitter and multiple receivers
- Ease of new system integration with minimal wiring
