Technical data

Table Of Contents
Glossary
System Software for S7-300/400 System and Standard Functions - Volume 2/2
Glossary-6
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Error, Synchronous
Synchronous errors are run-time errors assigned to a particular place in the user
program (for example, error accessing an I/O module). When these errors occur,
the operating system calls the corresponding organization blocks in which the user
can program a reaction.
Error, System Error
System errors are errors which may occur within a PLC (not in the process).
System errors can be, for example program errors in the CPU and faults in
modules.
Formal Parameter
A formal parameter is a placeholder for the actual parameter in logic blocks that
can be assigned parameters. In FBs and FCs, the formal parameters are declared
by the user; in SFBs and SFCs, they already exist. When a block is called, an
actual parameter is assigned to the formal parameter so that the called block works
with the latest value. The formal parameters belong to the local data of the block
and are declared as input, output, and in/out parameters.
Group Error
Error message indicated by a LED display on the front panel of modules (only) in
S7-300. The LED lights up whenever there is an error in the module concerned
(internal errors and external errors).
Hardware Interrupt
A hardware interrupt is triggered by modules with interrupt capability as a result of
a specific event in the process. The hardware interrupt is reported to the CPU. The
assigned organization block is then processed according to the priority of this
interrupt.
Input Parameter
Input parameters only exist in functions and function blocks. With the help of the
input parameters, data are transferred to the called block for processing.
Instruction
An instruction (STEP 5 or STEP 7) is the smallest part of a program created in a
textual language. It represents a command for the processor.