Siemens SIMATIC S5-90U System Manual page 176

STEP 5 Operations
Flip-Flop for a Latching Signal Output
A "1" at input I32.1 sets flip-flop Q32.5 (signal state "1").
If the signal state at input I32.5 changes to "0", the state of
output Q32.5 is maintained, i.e., the signal is latched.
A "1" at input I 32.0 resets the flip-flop (signal state "0").
When the "SET" signal (input I 32.1) and the "RESET"
signal (input I32.0) are applied at the same time, the
scanning operation that was programmed last (in this case
A I 32.0) is in effect during processing of the rest of the
program.
In this example, resetting output Q32.5 has priority.
STL
A I 32.1
S Q 32.5
A I 32.0
R Q 32.5
*
NOP 0
* "NOP 0" is necessary if the program is to be represented in LAD or CSF form on programmers with a screen.
NOP 0
During programming in LAD and CSF, such "NOP 0" operations are allotted automatically.
8-8
Example
CSF
Q32.5
I32.1
S
I32.0 R Q
S5-90U/S5-95U
Circuit Diagram
I32.0 I32.1
Q32.5
LAD
Q32.5
I32.1
S
I32.0
R Q
EWA 4NEB 812 6115-02b