HI-3200, HI-3201
ARINC 429 Bit ordering
ARINC 429 messages consist of a 32-bit sequence as
shown below. The first eight bits that appear on the ARINC
429 bus are the label byte. The next twenty three bits
comprise a data field which presents data in a variety of
formats defined in the ARINC 429 specification. The last bit
transmitted is an odd parity bit.
TheARINC 429 specifies the MSB of the label asARINC bit
1. Conversely, the data field MSB is bit 31. So the bit
significance of the label byte and data fields are opposite.
The HI-3200 may be programmed to “flip” the bit ordering of
the label byte as soon as it is received and immediately prior
to transmission. This is accomplished by setting the AFLIP
bit to a “1” in the Master Control Register. Note that once the
label byte has been flipped, the HI-3200 handles the flipped
data byte “post-flip” for the purpose of label interrupt
matching, filtering and storage.
The HI-3200 stores the received message as four bytes.
The bytes are stored in memory in little-endian order. That
is to say, the label byte (or status byte) is stored at the
lowest memory address, the byte representing received
bits 9 through 16 is stored at the next address, the byte
representing bits 17 through 24 at the next address and the
byte representing bits 25 though 32 at the highest address.
ARINC 429 Message as received / transmitted on the ARINC 429 serial bus
MSB
LABEL
LSB
LSB
DATA
MSB
ARITY
P
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
time
ARINC 429 Message as stored in HI-3200 memory
Byte 3
Byte 2
Byte 1
Byte 0
32 31 30 29 28 27 26 25
24 23 22 21 20 19 18 17
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
16 15 14 13 12 11 10
9
1
1
2
3
4
5
6
7
8
7
6
5
4
3
2
AFLIP = “0”
AFLIP = “1”
HOLT INTEGRATED CIRCUITS
21
HOLTIC [ HOLT INTEGRATED CIRCUITS ]
