DS_CTL_RW
ctl = octl | (mode & DS_CTL_RW);
ctl = (ctl & 0x3f) | (key & DS_CTL_RW);
ds1743_write(sc, DS_CENTURY, ((ds1743_read(sc, DS_CENTURY) & DS_CTL_RW)
bcdtobin(ds1743_read(sc, DS_CENTURY) & ~DS_CTL_RW) * 100;