Introduction.

Workshop PG5
Program structures
5.2 Program Blocks (PB 0 to 299)
What’s a PB:
You may also work with PB’s (Program Blocks). PB’s offer a good way to organize
your program in a hierarchical manner. PB’s are only activated if they are
called. They may be called from a COB or from another PB.
There are two ways to call a PB: Conditional call or unconditional call. Conditional
calls depend on the result of a logical operation. You can call the same PB several
times in the program. If one PB calls another PB and so on, then you can do so
up to seven levels.
A PB call can
be conditional
or unconditional:
COB 7
Enable input is always
high. Therefore the PB2
will be called in every
cycle => It's an unconditional
call
PB
PB
PB
PB
When the signal "move"
becomes high the PB is
called. This is a conditional
call.
Program blocks can not only be called from COB's, but also from PB’s, FB’s, or
SB’s.
© SAIA-Burgess Controls AG Page 5-3