Configuring Hardware and Communication Connections STEP 7.pdf

Synchronous Operation of Multiple CPUs (Multicomputing)
Address and Interrupt Assignment
In multicomputing mode the individual CPUs can access the modules assigned to
them during configuration with STEP 7. The address area of a module is always
exclusively assigned to a CPU.
All CPUs share the same address space; this means that the logical address of a
module is only present once in the multi-computing station.
An interrupt input is assigned to every CPU. Interrupts received at this input cannot
be received by the other CPUs. The assignment of the interrupt line is made
automatically during parameter assignment of the modules.
The following rules apply to interrupt servicing:
• Hardware interrupts and diagnostic interrupts are sent to only one CPU.
• If there is a module failure, the interrupt is serviced by the CPU to which the
module was assigned with STEP 7.
• If a rack fails, OB86 is called on every CPU.
You will find more detailed information on OB86 in the reference online help on
organization blocks.
8.1.2 When to Use Multicomputing
Multicomputing has advantages in the following situations:
• When your user program is too large for one CPU and memory is used up,
distribute your program among more than one CPU.
• If part of your system must be processed quickly, take these program sections
out of the main program and run them on a separate fast CPU.
• If your system consists of various parts that can be clearly delineated and can
be controlled relatively autonomously, run the program for system section 1 on
CPU 1 and system section 2 on CPU 2 etc.
Configuring Hardware and Communication Connections with STEP 7
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