Program Blocks (Pb); Sequence Blocks (Sbs); Program Blocks (Pbs) - Siemens SIMATIC S5 Manual

S5-115F Manual
2.3.2

Program Blocks (PBs)

Self-contained program parts are usually programmed in blocks.
Call
Block calls JU and JC activate program blocks. You can program these operations in all block types
except data blocks. Block call and block end cause the RLO to be reloaded. However, the RLO can
be included in the "new" block and evaluated.
The program counter (LPLZ) sequence contains the first operations for all PBs ( 3.8):
• LFW0
• LKF+1
• +F
• TFW0
The length of a PB is calculated as follows:
Operation code max.
+ Header
+ BE operation
If the PB is longer than 127 words (operation code), a "BLD 255 operation" with a program
counter sequence appended will appear at the latest in the 128th codeword. Interposed BLD 255
segmentation operations are unaffected by this.
2.3.3

Sequence Blocks (SBs)

Sequence blocks are special program blocks that process sequence controls. They are treated like
program blocks.
The program counter (LPLZ) sequence contains the first operations for all PBs ( 3.8):
• LFW0
• LKF+1
• +F
• TFW0
The length of a PB is calculated as follows:
Operation code max.
+ Header
+ BE operation
If the FB is longer than 127 words (operation code), a "BLD 255 operation" with a program
counter sequence appended will appear at the latest in the 128th codeword. Interposed BLD 255
segmentation operations are unaffected by this.
EWA 4NEB 811 6149-02
127 words
5 words
1 words
127 words
5 words
1 words
Introduction to STEP 5
2-13