M48T86_DOM
m48t86_writeb(dev, tm->tm_mday, M48T86_DOM);
m48t86_writeb(dev, bin2bcd(tm->tm_mday), M48T86_DOM);
tm->tm_mday = m48t86_readb(dev, M48T86_DOM);
tm->tm_mday = bcd2bin(m48t86_readb(dev, M48T86_DOM));