Programming Notes; Lplz Incrementing Sequence - Siemens SIMATIC S5 Manual

STEP 5 Operations
3.7

Programming Notes

In order to guarantee the safety of systems requiring official authorization, the possibility of
systematic errors by the user must be precluded. Systematic errors have the same effect on both
subunits.
Note
Organize your programs as clearly as possible!
The following are not permitted
• Trick programming
• Linking of Boolean logic operations to actions on different parentheses levels
The hardware does not monitor the parenthesis stack for overflow.
• The use of the operations DI, and JUR in safety-oriented programs.
3.8

LPLZ Incrementing Sequence

Operating system
Monitoring measures are integrated.
User program
An operation sequence for incrementing the logical program counter must be inserted at the
latest every 128 statements/operations in order to guarantee proper program execution in both
subunits.
The program is monitored by the logical program counter (LPLZ). It is located in FW 0 and must be
incremented by the user program at the latest after 127 codewords.
The following rule applies for structured programming with blocks:
• The sequence for incrementing the LPLZ is located at the beginning of each block
• Blocks longer than 127 words are segmented with "BLD 255"
• The BLD 255 operation before the 127 word boundary is followed by the LPLZ sequence
(10 bytes)
- LFW0
- LKF+1
- +F
- TFW0
• Flag word 0 must not be used by the user in any other way.
3-76
S5-115F Manual
EWA 4NEB 811 6149-02