I know for bigger installations the backplane bus is the bottleneck for the S7-300.
When having a lot of Profibus slaves (with a lof of communication per slave) connected to the online DP-interface Profibus cycle times can rise to high levels (one of my installations has 30ms, measured with diagnostic repeater, which I find too much). Dividing the network into two or more networks by adding a profibus mastercard in the rack would reduce the load per network and thus also the cycle time. But in case of a 300 controler maybe the new bottleneck will be the backplane bus. Maybe the effective time between transferring a value in the plc-programm and the receive in the Profibus slave migth be longer then when only using the integrated DP-master. I suppose that for a 400-controller that backplane load is neglectable.
What are your experiences, advices with using Dp-master cp's in a 300 or 400 rack and communication load, speed?
Thanks
When having a lot of Profibus slaves (with a lof of communication per slave) connected to the online DP-interface Profibus cycle times can rise to high levels (one of my installations has 30ms, measured with diagnostic repeater, which I find too much). Dividing the network into two or more networks by adding a profibus mastercard in the rack would reduce the load per network and thus also the cycle time. But in case of a 300 controler maybe the new bottleneck will be the backplane bus. Maybe the effective time between transferring a value in the plc-programm and the receive in the Profibus slave migth be longer then when only using the integrated DP-master. I suppose that for a 400-controller that backplane load is neglectable.
What are your experiences, advices with using Dp-master cp's in a 300 or 400 rack and communication load, speed?
Thanks
