retaining count value after power failure

Hi All

How do you retrieve a count value after a power failure or how do you prevent the value from clearing when the power fails.

Please Help

What PLC Brand? What Model? What Function are you using?

Always try and give as much information as possible so that people can help you.

Thanx usireland
I am using Siemens S7 313c and I am using statement list, I am using an up/down counter and the count value is transferred to a DB(is specified when you call the counter).

If you are using:

L Cxxx
T DBx.DBWxx

To put the counter value in the DB, then you can put in OB100:

L DBx.DBWxx
ITB
S Cxxx


If you use the following however:

LC Cxxx
T DBx.DBWxxx

You need to use the following in OB100:

L DBx.DBWxxx
S Cxxx


Using a simple L (load) you load the value as an INT.
Using the S (set preset value), the value needs to be BCD.
Hence the ITB (Int to BCD) in the first option.

Using LC (load as BCD), the value is already stored as BCD and you won't need the ITB.

Since you want to set the value after a power outage or a stop, the best way is to use OB100.
You can do it with a manually created first scan bit, but why re-invent the wheel?

NOTE: This is assuming you write the counter value to the DB continuously, ie every single scan.

Thanx Jeebs

I added OB100 to my program blocks and the problem was sorted.