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.

ARINC 429 data is transmitted between the HI-3593 and host

microcontroller using the four-wire Serial Peripheral Interface

(SPI). A read or write operation consists of a single-byte op-code

followed by the data. When writing to the transmit FIFO or reading

from the receive FIFOs, the SPI data field is four bytes. Figure 1

shows how the SPI data bytes are mapped to the ARINC 429

message.

ARINC 429 specifies the MSB of the label as ARINC 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-3593 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 TFLIP bit to a “1”

in the Transmit Control Register and/or the RFLIP bit in the

Receive Control Registers. The RFLIP bit does not control Priority

Label Match Registers.

Note that when reading ARINC 429 messages from the Priority-

Label Registers the label byte is omitted to permit a faster read

time. The label value will match the value loaded into the Match

Register and therefore does not need to be output each time a

message is read.

7

6

5

4

3

2

1

8

LSB

ARINC 429 Message as received / transmitted on the ARINC 429 serial bus

12 13

16

18 19

22 23

27

31

LABEL

DATA

MSB

LSB

MSB

time

ARINC 429 Message as transferred on the SPI bus

HI-3593

HOLT INTEGRATED CIRCUITS

8

15

14

11

10

9

21

20

28

25

32

17

24

26

29 30

0

29 28

25

23 22

19 18

14

10

SPI Op-Code

DATA

MSB

LSB

26

27

30

31

32

20

21

13

16

9

24

17

15

12 11

6

2

5

8

1

7

4 3

Example 1. Write Transmit FIFO (Op-Code 0x0C) with TFLIP bit = “0”.

000 11 00

LABEL

LSB

MSB

29 28

25

23 22

19 18

14

10

SPI Op-Code

DATA

MSB

LSB

26

27

30

31

32

20

21

13

16

9

24

17

15

12 11

6

2

5

8

1

7

4

3

Example 2. Read Receiver 1 FIFO (Op-Code 0xA0) with RFLIP bit = “1”.

00

1

00

LABEL

MSB

LSB

1

00

29 28

25

23 22

19 18

14

10

SPI Op-Code

DATA

MSB

LSB

26

27

30

31

32

20

21

13

16

9

24

17

15

12 11

Example 3. Read Receiver 2 Priority-Label Register #3 (Op-Code 0xCC).

0

1

00

1

0

11

SPI Op-Code

Example 4. Write Receiver 2 Priority-Label Match Registers (Op-Code 0x2C)with RFLIP bit = “1” or “0”.

00 0

1

0

11

0

LABEL #1

MSB

LSB

LABEL #2

MSB

LSB

LABEL #3

MSB

LSB

8

7

6

5

4

3

2

1

1

12

2

3

3

4

4

5

5

6

67

78

8

FIGURE 1.

ARINC 429 & SPI BIT ORDERING