MANTIS_I2CDATA_CTL
mmwrite(txd, MANTIS_I2CDATA_CTL);
data = mmread(MANTIS_I2CDATA_CTL);
mmwrite(rxd, MANTIS_I2CDATA_CTL);
rxd = mmread(MANTIS_I2CDATA_CTL);
mmwrite(txd, MANTIS_I2CDATA_CTL);