Information
46.4.3.1 Synchronous mode
The SAI transmitter and receiver can be configured to operate with synchronous bit clock
and frame sync.
If the transmitter bit clock and frame sync are to be used by both the transmitter and
receiver:
• The transmitter must be configured for asynchronous operation and the receiver for
synchronous operation.
• In synchronous mode, the receiver is enabled only when both the transmitter and
receiver are enabled.
• It is recommended that the transmitter is the last enabled and the first disabled.
If the receiver bit clock and frame sync are to be used by both the transmitter and
receiver:
• The receiver must be configured for asynchronous operation and the transmitter for
synchronous operation.
• 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.
46.4.4 Frame sync configuration
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
Functional description
K20 Sub-Family Reference Manual, Rev. 2, Feb 2012
1172 Freescale Semiconductor, Inc.