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OpAsync 429 MinorMajorFrame

Minor-Major Frames are used to perform scheduled transmission on ARINC-429bus. This feature is used in the OpAsync 429 Scheduled Major Frame and OpAsync 429 Scheduled Send blocks.


The frequency of messages transmission is defined in term of minor and major frames.

  • The major frame is the sequence that is looped indefinitely.
  • The major frame is decomposed into 'x' minor frames. The minor frames have the same duration and are numbered from 1 to 'x'.

For one scheduled message, the minor frame start, minor frame rate and scheduled time are defined.

For each channel, a scheduled major frame is defined by:

  • The minor frame duration
  • The number of minor frames during one major frame

A scheduled message is defined by:

Minor frame startDuring which minor frame, the message has to be sent first (from 1 to 'x')
Minor frame rateThe rate of repetition of the message. For instance, if the message has to be sent in each minor frame, this rate is '1'.
Scheduled timeThe time, relative to the start of the minor frame, that must be expired before the message is sent.

Usually for different periods of scheduled messages:

The minor frame time is the greatest common divisor of the different data rate periods. In many cases, this equals the period of the fastest data rate.
The number of minor frames per major frame equals the period of the slowest data rate divided by the minor frame time.


Third exampleThis example shows how to calculate the minor frame time and minor frame count, in the case where the periods of scheduled messages are not multiples of each other.
Two scheduled messagesL1 period 2ms
L1 period 3ms
One OpAsync_429_Scheduled_MajorFrame blockMinor frame time=1 ms
Minor frames count=6
One OpAsync_429_Scheduled_Send blockMinor rate=2, start minor frame=1, scheduled time=0
One OpAsync_429_Scheduled_Send blockminor rate=3, start minor frame=2, scheduled time=0.5ms for instance

Important Information

Successive transmissions constraintBe aware that the duration between two successive transmit messages on the same channel cannot be less than 360 µs.
Possible message loss

Some messages can be lost and the requested scheduled times will not be met if:

  • the user sets too many messages on the same minor frame
  • the difference between two scheduled times given for messages on the same minor frame is inferior to 360 us.
Disabling minor frame schedule timeIf the exact transmission of the different messages inside one minor frame is not important, the value '0' can be set to every 'scheduled time' in order to send the messages as soon as the previous transmission is finished.

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