Introduction.
Introduction.
Introduction.
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Workshop PG5<br />
Program structures<br />
5.1 Cyclic Organization Block (COB 0 to 15)<br />
What’s a COB:<br />
COB's (Cyclic organization blocks) are foreseen for program parts which are<br />
executed nonstop, without ever waiting stopping. (For example in order to wait<br />
for internal or external events to happen). After Startup of the PCD, the program<br />
starts executing the first COB in the program file and then executes one COB after<br />
the other. If needed you may create up to 16 COB’s. All the COB's are called<br />
automatically one after the other in a never ending cycle.<br />
All signals which need to be treated on a regular basis (for example end-switches for<br />
motor movements, external power-cut or emergency-stop signals, human protection<br />
devices ect) have to be inside a COB.<br />
There has to be at least one COB in the PCD!<br />
It is very important to understand, that the notion of the blocks which<br />
are always executed, is the most important aspect of all PLC's. The<br />
lack of waiting loops is not a failure in the concept of PLC programming,<br />
but a very important security feature. It's the only way you can<br />
guarantee your client that important signals are checked on a regular<br />
basis.<br />
If you write your programs with the “FUNCTION BLOCK EDITOR”, a new file in<br />
a COB is automatically opened for you.<br />
You can then change the block type or comment as you wish.<br />
In instruction list programs, the block is defined by instructions which surround the<br />
program code.<br />
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