ARINC429_Tutorial

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3.4.3 Data Data ARINC429 defines bits 11-29 as those containing the word’s data information. Formatting of the data bits, indeed the entire ARINC429 word, is very flexible. When transmitting data words on the ARINC bus, the Label is transmitted first, MSB first, followed by the rest of the bit field, LSB first. Bit transmission order looks like this: 8 7 6 5 4 3 2 1 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 Label SDI MSB Data LSB SSM P The Label is always transmitted first, in reverse order to rest of the ARINC word – a compensation for compatibility with legacy systems. The receiving LRU is responsible for data translation and regrouping of bits into proper order. Data types available in ARINC429 are: ± Binary – BNR – Transmitted in fractional two’s complement notation ± Binary Coded Decimal – BCD – Numerical subset of ISO Alphabet No. 5 ± Discrete Data – Combination of BNR, BCD or individual bit representation ± Maintenance Data and Acknowledgement – Requires two-way communication ± Williamsburg/Buckhorn Protocol – A bit-oriented protocol for file transfers 17 AIT - ARINC 429 Protocol
3.4.4 Data Types Data Types BNR Data Binary, or BNR, encoding stores data as a binary number. Bit 29 is utilized as the sign bit with a 1 indicating a negative number – or South, West, Left, From or Below. Bit 28 is then the data’s Most Significant Bit (MSB), or ½ of the maximum value of the defined parameters scale factor. Bit 27 is ½ the value of Bit 28 or ¼ of the scale factor. Bit 26 is ½ the value of Bit 27 or 1 / 8 the scale factor and so on. 32 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 P SSM MSB Data LSB SDI Label BCD Data Binary Coded Decimal, or BCD format uses 4 data field bits to represent each decimal digit. Up to 5 subfields can be utilized to provide 5 binary values, with the Most Significant subfield containing only 3 data field bits (for a maximum binary value of 7). If the Most Significant digit is greater than 7, bits 27-29 are padded with zeros and the second subfield becomes the Most Significant digit allowing 4 binary values instead of 5 to be represented. The SSM field is used to provide the sign of the value. 32 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 P SSM Digit 1 Digit 2 Digit 3 Digit 4 Digit 5 SDI Label Discrete Data Discrete data can be made up of BNR and/or BCD data, or as individual bits representing specific equipment conditions. Pass/Fail, Activated/Non-Activated and True/False conditions relating to system or subsystem operational activity can be represented by setting or clearing predefined bits in the word data field. Maintenance Data and Acknowledgement Maintenance Data and Acknowledgement implies duplex or two-way communication between source and sink. Since ARINC429 only provides for one-way simplex transmission, two ARINC channels are required for an LRU to send and receive data. Maintenance messages typically require exchanging a sequence of messages and often utilize a bit oriented protocol such as the Williamsburg/Buckhorn protocol. Williamsburg/Buckhorn Protocol Williamsburg/Buckhorn is a bit-oriented protocol used to transmit files across an AIT - ARINC 429 Protocol 18
Page 1: ARINC 429 Protocol Tutorial 3703 N.
Page 4 and 5: Omaha Office 3703 N. 200th Street,
Page 6 and 7: 1 About this Manual This manual was
Page 8 and 9: 2 ARINC429 Specification Overview T
Page 10 and 11: 2.2 History of ARINC429 The ARINC42
Page 12 and 13: A transmitter may require acknowled
Page 14 and 15: 3.2 Transmission Characteristics AR
Page 16 and 17: 3.3 Waveform Parameters Pulse rise
Page 18 and 19: 3.4 Word Formats ARINC429 protocol
Page 20 and 21: 3.4.2 Sign/Status Matrix Bits 31-30
Page 24 and 25: ARINC bus. Williamsburg has superce
Page 26 and 27: 3.4.6 Label Label Bits 1-8 contain
Page 28: 4 ARINC Contact Information A compl

ARINC429_Tutorial

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