Siemens SIMATIC S7-400 Hardware And Installation Manual page 116

Networking
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).
MPI
PG
Figure 5-2
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.
5-6
www.gkbpx.com
CPU
PLC
OS
Data Exchange
S7-400 and M7-400 Programmable Controllers, Installation Manual
PLC
OS
PG
SIMATIC NET
DP network
Slave
OS
PG
C79000-G7076-C424-01