Program Interface Library ARINC 429 Data Format
CEI-100/CEI-200/CEI-x20 User’s Manual 60
The ARINC 573/717 software interface on the CEI-420-70J and CEI-420-
xxJ is nearly identical to the ARINC 429 interface. It appears as channel 7
to the software (counting the first channel as channel 0). The 573 interface
on the CEI-520/520A-xxJ, CEI-620-xxJ, and CEI-820-xxJ appears as the
first channel. For all devices equipped with 573/717 support, the receiver
and transmitter configuration must be loaded by calling
AR_SETCHPARMS before normal operation can begin.
ARINC 429 Data Format
Formatting of ARINC 429 32-bit words can be confusing to first-time
ARINC users. This section will attempt to answer some common
questions about the formatting of ARINC words by the CEI-100/200/x20
boards. See our “ARINC Protocol Tutorial” (available at
http://www.abaco.com/download/arinc-protocol-tutorial) for a complete
discussion of ARINC word formats.
Label Formatting
The ARINC 429 specification calls for the ARINC label bits to be
transmitted on the ARINC bus in inverse order (bit 8 first, bit 1 last). The
CEI-100/200/x20 hardware works with labels that are formatted in the
normal bit order. During transmission, it automatically shifts the bits out
on the bus in the correct (inverted) order. During reception, it formats and
returns the bits in the proper order as well. There is no need for you to
invert the label before or after transmission.
Transmission Order
ARINC convention numbers the bits of an ARINC word from 1 (LSB) to
32 (MSB). The least significant bit of each byte (except the label) is
transmitted first; the label is transmitted ahead of the data in each case.
The order of the bits transmitted on the ARINC bus is as follows:
8,7,6,5,4,3,2,1,9,10,11,12,13 … 32.
Most applications work with ARINC words formatted in engineering
format; the bits are ordered from left to right, bits 32 … 1, where bit 32 is
the most significant bit (parity) and bit 1 is the least significant bit (least
significant bit of the label).
The CEI-100/200 boards provide a function (AR_REFORMAT) that
converts a transmit ARINC word into transmission format. This function
should be used to convert a transmit word before calling AR_PUTWORD
to transmit the word.
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