Aero Protocols

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Highlights Introduction to protocol

Overview of AFDX ARINC-429

CAN


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Introduction to Protocol

Agreement about the exchange of

information in a distributed system.

Protocol defines. precise formatfor valid messages(a syntax).

the procedure rules for the data exchange (a grammar).

a vocabularyof valid messages that can be exchanged, with their meaning (semantics).


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AFDX

Stands forAvionics Full DupleX Switched

Ethernet.

AFDX concepts introduced by Airbus.

Is based upon Ethernet.

Separated into. Avionics Subsystem.

AFDX End System (End System).

AFDX Interconnect.


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AFDX


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AFDX


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AFDX


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AFDX


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AFDX


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AFDX


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AFDX


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ARINC 429

Parity.

SSM.

DATA & PAD.

SDI

LABEL


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ARINC 429


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CAN

CAN stands forControllerArea Network.

CAN was first developed by Robert BoschGmbH, Germany in 1986.

The first CAN silicon was then fabricated in 1987by Intel

CAN STANDARDS Standard CAN (Version 2.0A). Uses 11 bit identifiers

Extended CAN (Version 2.0B). Uses 29 bit identifiers


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CAN

There are three types ofCAN controllers

Message format \ CAN chip type Part A Part BPassive Part B

11 bit ID ok ok ok

29 bit ID ERROR!! tolerated on the bus, but ignored ok


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CAN

11 BIT CAN Frame format


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CAN

29 BIT CAN Frame format


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CAN

Bit Timing


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CAN

ERRORClassification

Bit errors:

Bit stuffing error- normally a transmitting node inserts a high after five consecutive low bits(and a

low after five consecutive high). This is called bit stuffing. A receiving node that detects violation

(more than five consecutive bits will see a bit stuffing violation.

Bit error- A transmitting node always reads back the message as it is sending. If it detects a differentbit value on the bus than it sent, and the bit is not part of the arbitration field or in the

acknowledgement field, and error is detected.

Message errors:

Checksum error- each receiving node checks CAN messages for checksum errors.

Frame error- There are certain predefined bit values that must be transmitted at certain points within

any CAN Message Frame. If a receiver detects an invalid bit in one of these positions a Form Error

(sometimes also known as a Format Error) will be flagged.

Acknowledgement Error- If a transmitter determines that a message has not been ACKnowledged

then an ACK Error is flagged.


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CAN

CONTROLLERERROR STATES

The mode of the controller is controlled by two error counters

the transmit error counter (tx_count) and the receive error counter (rx_count). The

following rules apply:

The CAN controller is in error active mode if tx_count 127) AND tx_count 255.

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