How to do retentive memory in 313C-2DP

Hi,
I want to have a retentive marker word in a 313C-2DP. I have set up retentive memory in the properties of the PLC in the hardware config to be 16 bytes starting with MB0 but when I power the PLC down and back up it seems to lose whatever I've put in MW2 ?

I wondered if I need a battery for the PLC and (if so) where does the battery go ??

Many thanks for any light you can shed on this

;-)

There are several types of memory.

What's the order-nr of the cpu: 6ES7-?

Hi Ivo,
Sorry for the late reply, I've not been on the site for a few days.

My mistake, the retentive memory is working fine. I was viewing the wrong MW and the problem is sorted now.

It was a 314-6CG03-0AB0 by the way.

Thanks

;-)