46.6.6.7 Single Data Mode
In Single Data mode, only one data is written every time TWIHS_THR is accessed, and only one data is read every time TWIHS_RHR is accessed.
When TWIHS_FMR.TXRDYM = 0, the Transmit FIFO operates in Single Data mode.
When TWIHS_FMR.RXRDYM = 0, the Receive FIFO operates in Single Data mode.
See sections TWIHS_THR46.7.18 TWIHS Transmit Holding Register and TWIHS_RHR46.7.15 TWIHS Receive Holding Register.