NXP Semiconductors K22F series, Reference Manual, Page: 1368 / 1407

49.4.4 Frame sync configuration
When enabled, the SAI continuously transmits and/or receives frames of data. Each
frame consists of a fixed number of words and each word consists of a fixed number of
bits. Within each frame, any given word can be masked causing the receiver to ignore
that word and the transmitter to tri-state for the duration of that word.
The frame sync signal is used to indicate the start of each frame. A valid frame sync
requires a rising edge (if active high) or falling edge (if active low) to be detected and the
transmitter or receiver cannot be busy with a previous frame. A valid frame sync is also
ignored (slave mode) or not generated (master mode) for the first four bit clock cycles
after enabling the transmitter or receiver.
The transmitter and receiver frame sync can be configured independently with any of the
following options:
• Externally generated or internally generated
• Active high or active low
• Assert with the first bit in frame or asserts one bit early
• Assert for a duration between 1 bit clock and the first word length
• Frame length from 1 to 16 words per frame
• Word length to support 8 to 32 bits per word
• First word length and remaining word lengths can be configured separately
• Words can be configured to transmit/receive MSB first or LSB first
These configuration options cannot be changed after the SAI transmitter or receiver is
enabled.
49.4.5 Data FIFO
Each transmit and receive channel includes a FIFO of size 8 × 32-bit. The FIFO data is
accessed using the SAI Transmit/Receive Data Registers.
49.4.5.1 Data alignment
Data in the FIFO can be aligned anywhere within the 32-bit wide register through the use
of the First Bit Shifted configuration field, which selects the bit index (between 31 and 0)
of the first bit shifted.
Examples of supported data alignment and the required First Bit Shifted configuration are
illustrated in
Figure 49-3 for LSB First configurations and Figure 49-4 for MSB First
configurations.
Functional description
K22F Sub-Family Reference Manual, Rev. 4, 08/2016
1368 NXP Semiconductors