Siemens SIMATIC S5 Manual page 315

IP 266
The edge flag for programming the TOGGLE bit is also required (FB 25/FB 26).
START
Job in progress?
no
Evaluate auxiliary
and edge flags
Edge flag = 0?
no
Load bit 0 = 1
(QB 65) into FY 6
END
EWA 4NEB 812 6057-02
FB 21 - NAME:START
Programming the auxiliary and edge flags for the
START function
Job in progress abort
yes
AN I
BEC
Programming the edge and auxiliary flags
A I
AN F
= F
yes
A I
= F
Edge flag not yet set abort
AN F
BEC
Load Start command
L KB 1
T FY 6
BE
STEP 5 Programming
66.7
3.1 START KEY
4.0
4.1 EDGE FLAG
3.1 START KEY
4.0
4.1
START COMMAND
9-27