no initialisation of external memory

hello,

I use some external memory (xdata) for saving some information in external ram (with battery) before a shut off of my application,
but when I switch on the application all my xdata are set to 0 and don't stay with their last value.

I do this for the declaration of my external variable

in global.c
unsigned char xdata reglage0 _at_ 0x4001

and in global.h
external unsigned char xdata reglage0;

I do a include global.h in all my c file.

what can I do for resolving this problem?

tkx for your answer.