Siemens SINUMERIK 840D sl Function Manual page 175

Figure 2-28
Configuration limit
The diagram above illustrates how the communication overhead grows as the number of
NCUs increases.
Curve trace A:
Time required for the exchange of link variables/machine data information and the lead link
axis information (one lead link axis) between the NCU giving the master value and other
NCUs that interpolate the following axes as a function of the leading axis (lead link axis).
Curve trace B:
Time required for the exchange of link variables/machine data information between the NCU
giving the master value and other NCUs that interpolate the following axes as a function of
the leading axis (lead link axis).
Rule
In a configuration, the time requirement must remain below the interpolation cycle in
accordance with curve trace A. If it is not possible to alter the number of required NCUs, the
interpolation may have to be adapted if necessary.
If the interpolation cycle has to remain unchanged, the number of NCUs in the lead link axis
grouping may have to be reduced if necessary.
Extended Functions
Function Manual, 01/2008, 6FC5397-1BP10-3BA0
Several Operator Panels on Several NCUs, Distributed Systems (B3)
Increase in communication time of the number of NCUs connected via the link (for
scaling refer to Interdependencies)
2.10 Communication in link grouping
175