Multicomputing - Siemens SIMATIC S7-400 Configuration And Use Manual

CPUs of the S7-400
2.4

Multicomputing

Introduction
Multicomputing mode is the simultaneous operation of several (maximum of four)
CPUs in a single central controller of the S7-400.
The CPUs involved automatically change their modes synchronously. In other
words, they start up together and change to STOP mode together. The user
program runs on each CPU irrespective of the user programs in the other CPUs.
This makes it possible to execute controller tasks in parallel.
Multicomputing mode is not available with the CPUs of the S7-400H.
When do you use multicomputing?
It is advantageous to use multicomputing in the following cases:
• If your user program is too large for a single CPU and memory is limited, you
can distribute your program over several CPUs.
• If a certain part of your system is supposed to be processed quickly, separate
the relevant program section from the overall program and have it processed by
a dedicated, "fast" CPU.
• If your system consists of several different parts that can be easily separated
from one another and can therefore be controlled relatively independently, let
CPU1 process system part 1, CPU 2 system part 2 and so on.
Assigning Modules to the CPUs
In multicomputing mode, the individual CPUs can each access the modules that
were allocated to them during configuration with STEP 7. The address area of a
module is always assigned "exclusively" to one CPU.
Each interrupt-capable module is therefore assigned to a CPU. Interrupts
originating from such a module cannot be received by the other CPUs.
I/O Volume
The typical I/O volume of an automation system in multicomputing mode
corresponds to the volume of the CPU with the most resources
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Automation System S7-400 Configuration and Use
A5E00442711-02