S7-200 SMART
System Manual, V2.3, 07/2017, A5E03822230-AF
169
Program instructions
7
7.1
Bit logic
7.1.1
Standard inputs
LAD
FBD
STL
Description
LD bit
A bit
O bit
Test a bit value in memory (M, SM, T, C, V, S, L) or process image
register (I or Q).
LAD: Normally open and normally closed switches are represented
by a contact symbol. If power flow is present on the left-side and the
contact is closed, then power flows through the contact to the right-
side connector and to the next connected element.
•
The Normally Open (N.O.) LAD contact is closed (ON) when the
bit is equal to 1.
•
The Normally Closed (N.C.) LAD contact is closed (ON) when the
bit is equal to 0.
FBD: Normally open instructions are represented by AND/OR boxes.
Box instructions can be used to evaluate Boolean signals in the same
manner as ladder contact networks. Normally closed instructions are
also represented by boxes. A normally closed instruction is created
by placing the negation circle
, on a binary input sig-
nal connector. The number of inputs for the AND/OR boxes can be
expanded to a maximum of 31 inputs.
STL: The normally open contact is represented by the LD (load), A
(AND), and O (OR) instructions. These instructions load, AND, or OR
the value of the addressed bit with the top bit of the logic stack. The
normally closed contact is represented by the LDN (Load NOT), AN
(AND NOT), and ON (OR NOT) instructions. These instructions load,
AND, or OR the logical NOT of the addressed bit value with the top
bit of the logic stack.
LDN bit
AN bit
ON bit
Input / output
Data type
Operand
bit (LAD, STL)
BOOL
I, Q, V, M, SM, S, T, C, L,
Input (FBD)
BOOL
I, Q, V, M, SM, S, T, C, L, Logic flow
Output (FBD)
BOOL
I, Q, V, M, SM, S, T, C, L, Logic flow