SERIAL_RX_ON
readreg(dev, PP_LineCTL) | SERIAL_RX_ON | SERIAL_TX_ON);
readreg(dev, PP_LineCTL) & ~(SERIAL_TX_ON | SERIAL_RX_ON));
writereg(dev, PP_LineCTL, readreg(dev, PP_LineCTL) | SERIAL_RX_ON | SERIAL_TX_ON);