OBs

Hi all
If I want to use any OBs in the program how can I program it
I use an OB but I insert it without programming I want to know if this true or false
Thank you
Adel abd el aziz

OB's are called from the operating system of the cpu. You do not need to call them like an FC or FB.

Off course you must write code into OB1 if only a call to an FC or FB. As a matter of fact you can write 'all code' inside OB1.

Hi there
Refer to the link below
http://www.plctalk.net/qanda/showthread.php?t=31378

Diffrent OBs are called upon on occurance of a particular error. Example--> PLC calls OB121 when there is program execution error. You can write the following code inside the OB121:
L #OB121_SW_FLT
T MB 150

So when OB121 is called upon it will place a relavent error code value in byte MB150, for example if MB150 shows 21 then its BCD conversion error.For more details highlight OB121 and press F1.

Its not compulsory to programme OB's.

ivo.maenen said:

As a matter of fact you can write 'all code' inside OB1.

Click to expand...

Of course that would make you a really terrible programmer.

adel abd el aziz said:

Hi all
If I want to use any OBs in the program how can I program it
I use an OB but I insert it without programming I want to know if this true or false
Thank you
Adel abd el aziz

Click to expand...

Each OB is called from the system you do not need to call them.

Apart from OB1 you do not need to use any other OB unless you need the functionality. Read the documents on their function, some are timed, some are for first scan initialisation, some are for faults, etc, etc.

for any OBs to make her job I must programming it or not or if I select an OB like OB81 it do its job without programming

OB81 is a fault handling OB, if you do not have OB81 programmed and that fault occurs, then the PLC will go into STOP.

If OB81 is created and downloaded to the PLC, then the PLC will not go into STOP, the OB TEMP's will indicate the fault and your programming can be used toi determine if you would like to STOP the PLC or not.