M48T86_DOW
m48t86_writeb(dev, tm->tm_wday, M48T86_DOW);
m48t86_writeb(dev, bin2bcd(tm->tm_wday), M48T86_DOW);
tm->tm_wday = m48t86_readb(dev, M48T86_DOW);
tm->tm_wday = bcd2bin(m48t86_readb(dev, M48T86_DOW));