
Conventions for S7-200 Instructions
8-4
S7-200 Programmable Controller System Manual
C79000-G7076-C233-01
Operand Table: Beneath the LAD/FBD/STL figure is a table that lists the allowed
operands for each of the inputs and outputs, along with the data types of each
operand. The memory ranges of the operands for each CPU are shown in
Table 8-3.
EN/ENO operands and data types are not shown in the instruction operand table
because the operands are the same for all LAD and FBD instructions. Table 8-1
lists these operands and data types for LAD and FBD. These operands apply to all
LAD and FBD instructions shown in this manual.
Table 8-1 EN/ENO Operands and Data Types for LAD and FBD
Language
Editor
Inputs/Outputs Operands Data Types
LAD EN Power Flow BOOL
ENO Power Flow BOOL
FBD EN I, Q, M, S, SM, T, C, V, L, Power Flow BOOL
ENO I, Q, M, S, SM, T, C, V, L, Power Flow BOOL
General Conventions of Programming
Network: In LAD the program is divided into segments called networks. A network
is an ordered arrangement of contacts, coils, and boxes that are all connected to
form a complete circuit between the left power rail and the right power rail (no short
circuits, no open circuits, and no reverse power flow conditions exist).
STEP 7-Micro/WIN 32 allows you to create comments for your LAD program on a
network by network basis.
FBD programming uses the network concept for segmenting and commenting your
program. STL programs do not use networks; however, you can use the
NETWORK keyword to segment your program. If you do this, your program can be
converted to either LAD or to FBD.
Execution Subsections: In LAD, FBD, or STL a program consists of at least one
mandatory section and other optional sections. The mandatory section is the Main
Program. Optional sections can include one or more subroutines and/or interrupt
routines. You can easily move between subsections of the program by selecting or
clicking on the subsection tabs displayed by STEP 7-Micro/WIN 32.
EN/ENO Definition: EN (Enable IN) is a Boolean input for boxes in LAD and
FBD. Power flow must be present at this input for the box instruction to be
executed. In STL the instructions do not have an EN input, but the top of stack
value must be a logic “1” for the corresponding STL instruction to be executed.
ENO (Enable Out) is a Boolean output for boxes in LAD and FBD. If the box has
power flow at the EN input and the box executes its function without error, then the
ENO output will pass power flow to the next element. If an error is detected in the
execution of the box, then power flow is terminated at the box that generated the
error.
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