Specifications

Conventions for S7-200 Instructions
8-3
S7-200 Programmable Controller System Manual
C79000-G7076-C233-01
Title of the Instruction or Instruction Group: In this example Add Integer and
Subtract Integer is the title.
Figure Showing the Micro/WIN 32 Instruction: The figure below the instruction
title contains a picture of the LAD instruction element, the FBD instruction element
and for SIMATIC instructions, the STL instruction mnemonics and operands. In
some cases, the picture of the LAD and FBD instructions are the same, and only
one box containing both the LAD and FBD picture is shown (this is the case in this
example). The SIMATIC STL instruction mnemonics and operands always appear
in a separate box.
In the example, the LAD/FBD pictures have three inputs (inputs are always on the
left side of the picture) and two outputs (outputs are always on the right side of the
picture). In LAD there are two basic types of inputs and outputs. The first type of
input/output is a power flow input or output.
In LAD, which is patterned after Relay Ladder Logic Electrical Drawings, there is a
left power rail that is energized. In LAD, contacts that are closed allow energy to
flow through them to the next element and contacts that are open block that
energy flow. Any LAD element that can be connected to the left or right power rail
or to a contact has a power flow input and/or output.
In SIMATIC FBD, which does not use the concept of left and right power rails, the
term “power flow” is used to express the analogous concept of control flow through
the FBD logic blocks. The logic “1” path through FBD elements is called power
flow.
In LAD a power flow input or output is always exclusively power flow and cannot be
assigned to an operand. In FBD the origin of a power flow input and the destination
of a power flow output can be assigned directly to an operand.
In addition to power flow many, but not all, instructions have one or more input and
output operands. The allowed parameters for the operand inputs and outputs are
provided in the Inputs/Outputs table beneath the LAD/FBD/STL figure.
CPU Type: The instruction figure shows the CPUs that support the instruction. In
this example, the instruction is supported by the CPU 221, CPU 222, and
CPU 224.
Instruction Description: The text to the right of the instruction figure on
page 8-2 describes the operation of the instruction(s). In some cases there is a
description of the operation of the instruction for each language and in other cases
there will be a single description that applies to all three programming languages.
Note that IEC terminology is slightly different from SIMATIC terminology. For
example, a SIMATIC Count Up (CTU) is called an instruction; an IEC CTU is called
a function block.
Error Conditions that Set ENO = 0: If the LAD/FBD instructions have an ENO
output, this section lists the error conditions that result in ENO being set to a zero.
SM Bits Affected: If the instruction affects SM bits as a normal part of executing
the instruction, the bits affected and how they are affected are listed in this section.