Simatic Instruction Set; Iec 1131-3 Instruction Set - Siemens SIMATIC S7-200 System Manual

Basic Concepts for Programming an S7-200 CPU
4.4 Understanding the Differences between SIMATIC and IEC 1131-3
Instructions

SIMATIC Instruction Set

Most PLCs offer similar basic instructions, but there are usually small differences in
their appearance, operation, etc., from vendor to vendor. The SIMATIC instruction
set is designed for the S7-200 CPU. These instructions may look and operate
slightly differently when compared to similar instructions in another brand of PLC.
Consider these points when you select the SIMATIC instruction set:
SIMATIC instructions usually have the shortest execution times.
All three editors (LAD, STL, FBD) work with the SIMATIC instruction set.

IEC 1131-3 Instruction Set

The International Electrotechnical Commission is a worldwide organization that
develops global standards for all fields of electrotechnology. Over the last several
years, the commission has developed an emerging standard that specifically
relates to many aspects of PLC programming. This standard encourages different
PLC manufacturers to offer instructions that are the same in both appearance and
operation. There are a few key differences between the SIMATIC instruction set
and the IEC1131-3 instruction set.
The IEC 1131-3 instruction set is restricted to those instructions that are
standard among PLC vendors. Some instructions that are normally included in
the SIMATIC set are not standard instructions in the IEC 1131-3 specification.
(These are still available for use as non-standard instructions, but if you use
them, the program is no longer strictly IEC 1131-3 compatible).
Some box instructions accept multiple data formats. This practice is often
referred to as overloading. For example, rather than have separate ADD_I (Add
Integer) and ADD_R (Add Real), math boxes, the IEC 1131-3 ADD instruction
examines the format of the data being added, and automatically chooses the
correct instruction in the CPU. This can save valuable program design time.
When you use the IEC 1131-3 instructions, the instruction parameters are
automatically checked for the proper data format. The data format checking is
not obvious to the user. For example, if you tried to enter an integer value for an
instruction that expected a bit value (on/off), an error results. This feature helps
to minimize programming syntax errors.
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S7-200 Programmable Controller System Manual
A5E00066097-02