Specifications

Basic Concepts for Programming an S7-200 CPU

4-11

S7-200 Programmable Controller System Manual

C79000-G7076-C233-01

The main points to consider when you select IEC 1131-3 instructions are:

 It is usually easier to learn how to create programs for different brands of PLCs.

 Fewer instructions are available (as specified by the standard) but you can

always use many of the SIMATIC instructions as well.

 Some instructions operate differently than their SIMATIC counterparts (timers,

counters, multiply, divide, etc.)

 These instructions may have longer execution times.

 These instructions can only be used within the LAD and FBD editors.

 IEC 1131-3 specifies that variables must be declared with a type and supports

system checking of data type.

SIMATIC and IEC 1131-3 Variable Data Types

Every SIMATIC and IEC 1131-3 instruction or parameterized subroutine is

identified by a precise definition referred to as a signature. For all standard

instructions, the allowable data types for each instruction operand is obtained from

the signature. For parameterized subroutines, the signature of the subroutine is

created by the user through the Local Variable Table.

STEP 7-Micro/WIN 32 implements simple data type checking for the SIMATIC

mode, and strong data type checking for the IEC 1131-3 mode. When a data type

is specified for either a local or global variable, STEP 7-Micro/WIN 32 ensures that

the operand data type matches the instruction signature to the level specified.

Table 4-2 defines elementary data types and Table 4-3 shows complex data types

available in STEP 7-Micro/WIN 32.

Table 4-2 IEC 1131-3 Elementary Data Types

Elementary Data Types

Description Data Range

BOOL Boolean 0 to 1

BYTE Unsigned byte 0 to 255

WORD Unsigned integer 0 to 65,535

INT Signed integer -32768 to +32767

DWORD Unsigned double integer 0 to 2

- 1

DINT Signed double integer -2

to +2

- 1

REAL IEEE 32-bit floating point -10

to +10