s7 200 plc connected to siemens hmi

i have plc s7 200 connected to Siemens Hmi TP266-6
The screen lose its value when the power is off for more than 3 days
although when we come from the weekly holiday that is friday and saturday we find all data.
what is the problem.
how can i take all the online values of the variables that are tag in the hmi. as when the screen lose its value i can download these variable directly to the hmi
as in s7 300 i can take all online datablock values in my offline program and in the case of lose data i download these datablock that i take before