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• In synchronous mode, the transmitter is enabled only when both the receiver and
transmitter are both enabled.
• It is recommended that the receiver is the last enabled and the first disabled.
When operating in synchronous mode, only the bit clock, frame sync, and transmitter/
receiver enable are shared. The transmitter and receiver otherwise operate independently,
although configuration registers must be configured consistently across both the
transmitter and receiver.
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 32 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.
Chapter 49 Integrated Interchip Sound (I2S) / Synchronous Audio Interface (SAI)
K20 Sub-Family Reference Manual, Rev. 1.1, Dec 2012
Freescale Semiconductor, Inc.
Preliminary
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