NXP Semiconductors K22F series, Reference Manual, Page: 1369 / 1407

Figure 49-3. SAI first bit shifted, LSB first
Figure 49-4. SAI first bit shifted, MSB first
49.4.5.2 FIFO pointers
When writing to a TDR, the WFP of the corresponding TFR increments after each valid
write. The SAI supports 8-bit, 16-bit and 32-bit writes to the TDR and the FIFO pointer
will increment after each individual write. Note that 8-bit writes should only be used
when transmitting up to 8-bit data and 16-bit writes should only be used when
transmitting up to 16-bit data.
Writes to a TDR are ignored if the corresponding bit of TCR3[TCE] is clear or if the
FIFO is full. If the Transmit FIFO is empty, the TDR must be written at least three bit
clocks before the start of the next unmasked word to avoid a FIFO underrun.
Chapter 49 Integrated Interchip Sound (I2S) / Synchronous Audio Interface (SAI)
K22F Sub-Family Reference Manual, Rev. 4, 08/2016
NXP Semiconductors 1369