I am using the DS1643
which contain both non voliate ram and a RTC.

In my project, i use the timer 1 interrupt to counter the machine operation time:
unsigned char second, min, hour;

//Keil C51 code
XBYTE[0x1ffe0]=second;
XBYTE[0x1ffe1]=min;
XBYTE[0x1ffe2]=hour;

Also, i have a function to recall the NVram data to the counter variavle.

it is not problem for the reset the system, and all data can be keep.

however, when i remove the power supply,
all data are going wrong.
P.S. No problem for the RTC, THE clock can run after power off, but the data was loss when power off.

How can i solve this problem?
any programming skills needed for using NVRAM?

Pls help!!!!!!!!!!!!!!!!
many thx!!!!!!!!!!!!!!