Abaco ARINC429 Special Considerations

Description

This document aims to address the considerations that must be taken into account when using certain encoding type combinations and/or when defining signals' parameters for a given ARINC-429 message.

BNR Considerations

The "Size" parameter value (number of bits) of this ARINC-429 driver for a given BNR signal translation always includes the sign bit (both for single and mixed BNR signal types). Notice that, per ARINC convention, the "Digits" value does not include the sign bit when the signal is a single BNR signal (not mixed).

Example:

For a signed BNR signal

Range (-256:255) and a resolution of 0.25 we can calculate the following values:

resolution = scale * 1/(2^Digits)
Digits = 10
scale = 256

The configuration parameters for this signal would then be:

Start bit: 28
Size: 11
Min: -256
Max: 255

For a un-signed BNR signal

Range (0:512) and a resolution of 0.25 we can calculate the following values:

resolution = scale * 1/(2^Digits)
Digits = 11
scale = 512

The configuration parameters for this signal would then be:

Start bit: 28
Size: 11
Min: 0
Max: 511.75

Notice how the Size parameter always refers to the total number of actual bits needed for the correct signal representation while Digits excludes the sign bit from the count

BCD Considerations

BCD signals, by definition, are divided into groups of 4 bits, however, when the Size" parameter of the signal is not a multiple of 4, special considerations must be taken regarding the Most Significant Digit (MSD) value.

Example:

For Size = 8: MSD max value = 9 (binary 1001)
For Size = 7: MSD max value = 7 (binary 111)