hello every one;
I need a ds1643 read&write clock examples
i read the date is ok.but i write them it wrong .the program is fllow

mov dptr,#control_clock
mov a,#0x80
movx @dptr,a

mov dptr,#clock_year
mov a,#0x30
movx @dptr,a
...

mov dptr,#control_clock
mov a,#0
movx @dptr,a

minute and second can change,other can't ,why

please give me a examples.
thank you very much
good luck for you