DS_CENTURY
octl = ds1743_read(sc, DS_CENTURY);
ds1743_write(sc, DS_CENTURY, ctl); /* Lock RTC for both reading and writing */
ctl = ds1743_read(sc, DS_CENTURY);
ds1743_write(sc, DS_CENTURY, ctl); /* Enable updates */
ds1743_write(sc, DS_CENTURY, ((ds1743_read(sc, DS_CENTURY) & DS_CTL_RW)
bcdtobin(ds1743_read(sc, DS_CENTURY) & ~DS_CTL_RW) * 100;