Profinet can be understood as a relatively special highway (such as the highway I saw in Indonesia), which is divided into three lanes: passing lane, driving lane, motorcycle lane… Then we often see Profinet IRT, Profinet RT corresponds to passing lanes and driving lanes. In addition, the Profinet we are talking about also has a standard TCP/IP level corresponding to motorcycle lanes…
Everyone who has driven a car knows that, in terms of priority, overtaking lane> driving lane> motorcycle lane. Then IRT is called “isochronous real-time” in professional terms, which means that it is “absolute” real-time; while RT does not have the “isochronous” blessing, so it can only be called ordinary real-time, which means it is occasionally not real-time (for example, I set Set the RT cycle to 2ms, so in fact, occasionally there are no data exchanges in 2ms), and TCP/IP is not to mention, there is no real-time performance at all!
(Below for convenience, I set the period of IRT and RT to 2 milliseconds, and at the same time set the management cycle time of the toll collector to 20S, assuming the two are the same)
Then the three priority levels are all managed by the CPU. This management organization is a bit similar to a highway toll booth: Various cars come in front of the toll booth at any time, and the toll collector lets the cars passing the lane pass first; The lane arrangement is completed, and it is less than 20s. At this time, the administrator will let the traffic lane pass; if the lane is over, if it is less than 20s, then arrange the motorcycle to pass.
In the above management process, there will be various emergencies. For example, there are more cars passing the lane in a certain 20S cycle. At this time, the cars in the lane may not be queued in this cycle and have to wait until the next cycle. …This is how RT may not be real-time…
Next, are Profinet IO and Profinet RT the same thing? Most of the information basically defaults that these two are one level, that is, we configure a 1500+ET200SP remote IO, and the general habit is that ET200SP chooses RT! In most cases, it is enough! So the general default is Profinet IO = Profinet RT level. But this statement is not rigorous. For example, I can also set the ET200SP to IRT mode (some special processes must require IRT mode, such as attaching a time stamp module to the ET200SP, or attaching a position module to participate in motion control, etc.) …. .. .
PLC ONE 