Siemens SIMATIC S5-95F Manual page 151

Introduction to STEP 5
The program uses block calls to exit one block and jump to another. You can therefore nest pro-
gram, function, and sequence blocks (see section 7.3) randomly in up to 16 levels.
Note
When calculating the nesting depth, note that the system program in the programmable
controller can call an organization block under certain circumstances (e.g. OB3, OB13;
OB2 does not influence the nesting depth).
The total nesting depth is the sum of the nesting depths of cyclic (OB1), interrupt-controlled (OB3),
and time-driven (OB13) program processing. If nesting goes beyond 16 levels, the PLC goes into
the "STOP" mode with the error message "STUEB" (block stack overflow).
OB1
Level 1
7-6
Level 2 Level 3
Figure 7-2. Nesting
. . . . . . .
. . . . . . .
. . . . . . . Level 16
EWA 4NEB 812 6210-02
S5-95F