Capturing and analyzing ARINC 429 with PicoScope

ARINC 429, also known as the Mark 33 DITS specification, was developed to provide interchangeability and interoperability of line replaceable units (LRUs) in commercial aircraft. ARINC 429 defines the physical and electrical interfaces of a two-wire data bus and the data protocol to support an aircraft's avionics local area network.

The physical connection wires are twisted pairs carrying balanced differential signaling. Data words are 32 bits in length and most messages consist of a single data word. Messages are transmitted at either 12.5 or 100 kbit/s. The transmitter constantly transmits either 32-bit data words or the NULL state. Most ARINC messages contain only one data word consisting of either binary (BNR), binary coded decimal (BCD), or alphanumeric data encoded using ISO Alphabet No. 5. File data transfers that send more than one word are also allowed.

ARINC 429 employs several techniques to minimize electromagnetic interference (EMI) with on-board radios and other equipment.

In addition to twisted-pair cabling, ARINC signaling defines a 10 V peak differential signal, with acceptable voltage rise and fall times for the Data A and Data B levels, and complementary differential bipolar return-to-zero (BPRZ) data encoding to minimize EMI emissions from the cable itself.

ARINC 429 data words are made up of five primary fields:

• Parity – 1 bit
• Sign/Status Matrix (SSM) – 2 bits
• Data – 19 bits
• Source/Destination Identifier (SDI) – 2 bits
• Label – 8 bits

Although ARINC 429 word transmission begins with Bit 1 and ends with Bit 32, ARINC 429 words are typically shown in the order from Bit 32 to Bit 1.

The first step is to acquire the ARINC word of interest using PicoScope. Then select Serial Decoding from the Tools menu.

Click Create and select ARINC 429 from the list of available protocols.

In the ARINC 429 configuration menu select the appropriate PicoScope input channel, baud rate and any other parameters as necessary. Click OK to see the decoded ARINC 429 messages in the PicoScope graph display.

For more information on PicoScope's serial decoding capabilities, see Serial bus decoding and protocol analysis - overview.