Siemens SINUMERIK 840D sl Function Manual page 74

Several Operator Panels on Several NCUs, Distributed Systems (B3)
2.1 Brief Description
Figure 2-1 Topology of distributed system configurations
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PLC-PLC communication entails one of the following:
- PLC-PLC cross-communication master, slave comm.)
or
- Local PLC I/Os
Function Manual, 01/2008, 6FC5397-1BP10-3BA0
Extended Functions