Specifications

Conventions for S7-200 Instructions
8-5
S7-200 Programmable Controller System Manual
C79000-G7076-C233-01
In SIMATIC STL, there is no ENO output, but the STL instructions that correspond
to the LAD and FBD instructions with ENO outputs do set a special ENO bit. This
bit is accessible with the STL instruction AENO (AND ENO), and may be used to
generate the same effect as the ENO bit of a box.
Conditional/Unconditional Inputs: In LAD and FBD, a box or a coil that is
dependent upon power flow is shown without a connection to any element on the
left side. A coil or box that is independent of power flow is shown with a connection
directly to the left power rail. Both conditional and unconditional inputs are shown
in Figure 8-1.
NEXT
JMP Instruction that is dependent on power flow
Instruction that is independent of power flow
FBD
JMP
NEXT
LAD
Figure 8-1 LAD Diagram of Conditional and Unconditional Inputs
Instructions without Outputs: Boxes that cannot cascade are drawn with no
Boolean outputs. These include subroutine calls, JMP, CRET, etc. There are also
ladder coils that can only be placed on the left power rail. These include LBL,
NEXT, SCR, SCRE, etc. These are shown in FBD as boxes and are distinguished
with unlabeled power inputs and no outputs.
Compare Instructions: SIMATIC FBD, IEC Ladder, and IEC FBD compare
instructions are shown as boxes although the operation is performed as a contact.
The compare instruction is executed regardless of the state of power flow. If power
flow is false, the output is false. If power flow is true, the output is set depending
upon the result of the compare.