Cyclic Data and Drives?

So I'm kind of a noob when it comes to PLCs and am curious about the communication between controllers and drives.

I've heard the term cyclic data or cyclic communications thrown around, but I'm not sure if I know exactly what it means. Does cyclic data simply refer to data that is updated/recorded/read during every scan of the PLC? Also, is that how a drive, VFD for example, communicates with a controller when monitoring parameter values of the drive?

I'm sure every controller and drive configuration is different, but maybe someone could explain this?

tomizzo11 said:

Does cyclic data simply refer to data that is updated/recorded/read during every scan of the PLC?

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No, just a relatively constant intervals and usually this cyclic update is done automatically. For instance Profibus usually updates much faster than the PLC scan whereas Ethernet update are usually slower.

Also, is that how a drive, VFD for example, communicates with a controller when monitoring parameter values of the drive?

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I think it is the best way.

I'm sure every controller and drive configuration is different, but maybe someone could explain this?

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Yes, but they are usually similar in how they approach the problem.

I'll argue a detail there: Usually the Command and Status information from something like an AC drive is done over a cyclic data connection.

That's a relatively small amount of data (usually a handful of bytes) that needs to be updated quickly and reliably.

Online monitoring of VFDs and motion controllers and similar devices generally requires reading a handful of parameters scattered throughout the memory structure of the drive, and doing so on command (like when Uploading) or infrequently. This sort of traffic is called 'unsolicited' or 'unscheduled'.

Many AC drives or motion controllers have an option to add a small number of selectable parameters to the cyclic I/O connection, so that they are updated more frequently.