Siemens SIMATIC S5-100U System Manual page 128

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 randomly up to 16 levels (see section 7.3). Nesting can be up
to 32 levels for CPU 103 version 8MA03.
Note
When calculating the nesting depth, note that the system program in the programmable
controller can call an organization block automatically under certain circumstances
(e.g., OB2).
The total nesting depth is the sum of the nesting depths of call programmed organization blocks. If
nesting goes beyond 16 levels (32 levels for CPU 103 version 8MA03), the CPU goes into the
STOP mode with the error message "STUEB," block stack overflow (see section 5.2). Figure 7-2
illustrates the nesting principle.
OB 1
Level 1
Figure 7-2. Nesting Depth of Programmed Organization Blocks
7-6
Level 2 Level 3
. . . . . . .
. . . . . . .
. . . . . . . Level 16
EWA 4NEB 812 6120-02b
S5-100U