Chapter 9. Configuring the I/O Driver with the Power Tool 149
In situations where the mode of transmission is slow, such as radio or telephone
communication, we recommend phasing one or more datablocks to prevent overruns.
Overruns can occur when the driver attempts to process (read data from) more
datablocks at one time than it can update within the specified poll rate. By using
phasing, you can stagger when the driver processes a datablock.
Example
The following table shows an example of 10 datablocks processing every 10 seconds.
Name Primary Poll Rate Phase
Datablock0 10 0
Datablock1 10 1
Datablock2 10 2
Datablock3 10 3
Datablock4 10 4
Datablock5 10 5
Datablock6 10 6
Datablock7 10 7
Datablock8 10 8
Datablock9 10 9
The driver processes the first datablock immediately after starting up. Each subsequent
datablock message is processed one second later, instead of all at once.
NOTE: When transmission errors, retries, or other errors occur, the phasing you set may not
remain consistent. You may have to stop and restart the driver.
When phasing a datablock, also make sure its primary poll rate is longer than its phase.
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