Networking
5-6
S7-400 and M7-400 Programmable Controllers, Installation Manual
C79000-G7076-C424-01
PG Access
A CPU exchanges data with other systems using communication mechanisms, for
example with other programmable controllers, with operator interface stations (OP,
OS) or with programming devices (see Figure 5-2).
CPU
SIMATIC NET
MPI
PG
OS
PLC
PG
OS
Slave
PG
OS
PLC
DP network
Figure 5-2 Data Exchange
Process communication, including communication services for data exchange
between programmable controllers (PLC – PLC) and between programmable
controllers and operator interface stations (PLC – OS/OP), has priority in CPUs
over communication between programming devices and CPUs.
The CPUs have different characteristics. One of these characteristics is their
communication performance. If the communication resources of a CPU are
occupied completely by process communication, this can severely hamper access
to the CPU from the programming device.
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