When reading an RDR, the RFP of the corresponding RFR increments after each valid
read. The SAI supports 8-bit, 16-bit and 32-bit reads from the RDR and the FIFO pointer
will increment after each individual read. Note that 8-bit reads should only be used when
receiving up to 8-bit data and 16-bit reads should only be used when receiving up to 16-
bit data.
Reads from an RDR are ignored if the corresponding bit of RCR3[RCE] is clear or if the
FIFO is empty. If the Receive FIFO is full, the RDR must be read at least three bit clocks
before the end of an unmasked word to avoid a FIFO overrun.
40.5.5.3 FIFO packing
FIFO packing supports storing multiple 8-bit or 16-bit data words in one 32-bit FIFO
word for the transmitter and/or receiver. While this can be emulated by adjusting the
number of bits per word and number of words per frame (for example, one 32-bit word
per frame versus two 16-bit words per frame), FIFO packing does not require even
multiples of words per frame and fully supports word masking. When FIFO packing is
enabled, the FIFO pointers only increment when the full 32-bit FIFO word has been
written (transmit) or read (receive) by software, supporting scenarios where different
words within each frame are loaded/stored in different areas of memory.
When 16-bit FIFO packing is enabled for transmit, the transmit shift register is loaded at
the start of each frame and after every second unmasked transmit word. The first word
transmitted is taken from 16-bit word at byte offset $0 (first bit is selected by
TCFG5[FBT] must be configured within this 16-bit word) and the second word
transmitted is taken from the 16-bit word at byte offset $2 (first bit is selected by
TCSR5[FBT][3:0]). The transmitter will transmit logic zero until the start of the next
word once the 16-bit word has been transmitted.
When 16-bit FIFO packing is enabled for receive, the receive shift register is stored after
every second unmasked received word, and at the end of each frame if there is an odd
number of unmasked received words in each frame. The first word received is stored in
the 16-bit word at byte offset $0 (first bit is selected by RCFG5[FBT] and must be
configured within this 16-bit word) and the second word received is stored in the 16-bit
word at byte offset $2 (first bit is selected by RCSR5[FBT][3:0]). The receiver will
ignore received data until the start of the next word once the 16-bit word has been
received.
The 8-bit FIFO packing is similar to 16-bit packing except four words are loaded or
stored into each 32-bit FIFO word. The first word is loaded/stored in byte offset $0,
second word in byte offset $1, third word in byte offset $2 and fourth word in byte offset
$3. The TCFG5[FBT] and/or RCFG5[FBT] must be configured within byte offset $0.
Functional description
KL27 Sub-Family Reference Manual , Rev. 5, 01/2016
818
Freescale Semiconductor, Inc.
Содержание MKL27Z128VFM4
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