Siemens S7-400 installation manual PG Access, Data Exchange

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).

PG

OS

PLC

SIMATIC NET

CPU

MPI

PG OS PLC

		DP network
PG	OS		Slave

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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