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pairs served as “clock”, “sync”, and “data” respectively. Non return to
zero (NRZ) was employed, and a twelve-volt logic level was transmitted
for a binary 1. The word length was 32 bits. Bits 32 and 31 contained the
SSM, and no parity bit was provided. The remaining fields included an 8-
bit label and 6 BCD fields, five of 4 bits and one of 2 bits. In 1967 the sixwire
system was adopted as an industry standard.
Figure 9. ARINC 561 6-Wire Bit Encoding
ARINC 573
Other standards include ARINC 573, a Flight Data Recorder output format.
This device sends a continuous data stream of Harvard Bi-Phase encoded
12 bit words which is encoded in frames. The data in a frame consists of a
snapshot of the many avionics subsystems on the aircraft. Each frame
contains the same data at a different snapshot in time.
Other ARINC Protocols ARINC 575
ARINC Protocol Tutorial 21
Each frame is broken into four sub-frames. At the start of each sub-frame
is a unique sync word that is used by the receiver to synchronize with the
incoming data.
0v
5v
1 1 0 0 1 0 1 0
1 bit cell
Figure 10. Harvard Bi-phase Bit Encoding
ARINC 575
ARINC 575 is an older specification very similar to ARINC 429 but now
obsolete. It accommodated the Mark 3 Subsonic Air Data System (DADS)
with a single twisted pair of wires, which has become the standard in
ARINC 429. Electrically, ARINC 575 is generally compatible with low
speed ARINC 429. Some variants of 575 use a bit rate that is significantly
slower than ARINC 429 and are not electrically compatible. Also, in some
cases, ARINC 575 words use bit 32 as parity (as does ARINC 429); in
other cases bit 32 is used as data.
ARINC 582
This is an older specification that has many electrical permutations. There
are 6-wire versions (see ARINC 561), 2-wire versions (see ARINC 575) as
well as 16-bit, 2-wire versions.
ARINC 615
Special cases of ARINC 429 compliant systems also exist. ARINC 615
(See Reference 8) describes a high-speed data loader to transfer
information to and from on board digital systems. It is a software protocol
layered on top of an ARINC 429 physical layer. There are two versions of
the loader. PDL is a portable flight line piece of test equipment and ADL
is designed to fit in commercial aircraft instrument panels. Both equipment
are capable of reading and writing to 3½ inch diskettes and transferring
ARINC 629 Other ARINC Protocols
22 ARINC Protocol Tutorial
data between the diskettes and a selected airborne computer. The transfers
can occur automatically, or via an ARINC 429 data bus. Data can be either
uploaded or downloaded as desired.
ARINC 629
Additional ARINC standards are being developed. ARINC 629 is used on
the new Boeing 777 Aircraft. It uses a high-speed bi-directional bus
capable of either periodic or aperiodic transmissions. Access to the bus is
controlled by a sophisticated protocol involving wait periods, quiet periods
and other rules. Further details can be found in Reference 9.
ARINC 708
This protocol is specific to airborne weather radar systems. It is used as the
output from the radar to the radar display. The bus uses 2-wires, is
simplex, Manchester encoded and runs at a one-megabit data rate. It was
originally based upon a simple derivative of MIL-STD-1553 technology.
The data words are 1600 bits long which is composed of one, 64-bit status
word and 512, 3-bit data words.
ARINC 717
ARINC 717 supercedes ARINC 573 and is used to perform the same
function. It adds a number of different bit rates and frame sizes. It also
provides for an alternate output data stream that is identical to the primary,
Harvard Bi-phase encoded stream, except that it is encoded in BPRZ
format (the same as ARINC 429).
ARINC Protocol Tutorial 23
APPENDIX A
References
List of References
ARINC Web Site, http://www.arinc.com
ARINC Specification 429P1-15, September 1, 1995
ARINC Specification 429P2-15, March 6, 1996
“Principles of Avionics Data Buses”, Editorial Staff of Avionics,
Communications Inc., Leesburg, VA
AEEC Letter 97-013/WIL-03, January 24, 1996
ARINC Digital Data System Compendium, ARINC Report 419-3,
November 5, 1984
ARINC Airborne Computer Data Loader, ARINC Report 615-2, June
1, 1991
“ARINC 629 P1-4 Multi-Transmitter Data Bus”, “Part1, Technical
Description”, December, 1995
Aeronautical Radio, Inc., 2551 Riva Road, Annapolis, MD, 21401
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