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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.
Definition
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 start | During which minor frame, the message has to be sent first (from 1 to 'x') |
|---|---|
| Minor frame rate | The rate of repetition of the message. For instance, if the message has to be sent in each minor frame, this rate is '1'. |
| Scheduled time | The 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.
Examples
| Third example | This 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 messages | L1 period 2ms L1 period 3ms |
| One OpAsync_429_Scheduled_MajorFrame block | Minor frame time=1 ms Minor frames count=6 |
| One OpAsync_429_Scheduled_Send block | Minor rate=2, start minor frame=1, scheduled time=0 |
| One OpAsync_429_Scheduled_Send block | minor rate=3, start minor frame=2, scheduled time=0.5ms for instance |
| |
Important Information
| Successive transmissions constraint | Be 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:
|
| Disabling minor frame schedule time | If 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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