Note
Care must be taken when expecting data from a master while
the slave is in a Wait mode or a Stop mode where the peripheral
bus clock is stopped but internal logic states are retained. Even
though the shift register continues to operate, the rest of the SPI
is shut down (that is, an SPRF interrupt is not generated until an
exit from Stop or Wait mode). Also, the data from the shift
register is not copied into the SPIx_DH:SPIx_DL registers until
after the slave SPI has exited Wait or Stop mode. An SPRF flag
and SPIx_DH:SPIx_DL copy is only generated if Wait mode is
entered or exited during a transmission. If the slave enters Wait
mode in idle mode and exits Wait mode in idle mode, neither an
SPRF nor a SPIx_DH:SPIx_DL copy occurs.
31.4.11.3 SPI in Stop mode
Operation in a Stop mode where the peripheral bus clock is stopped but internal logic
states are retained depends on the SPI system. The Stop mode does not depend on
C2[SPISWAI]. Upon entry to this type of stop mode, the SPI module clock is disabled
(held high or low).
• If the SPI is in master mode and exchanging data when the CPU enters the Stop
mode, the transmission is frozen until the CPU exits stop mode. After the exit from
stop mode, data to and from the external SPI is exchanged correctly.
• In slave mode, the SPI remains synchronized with the master.
The SPI is completely disabled in a stop mode where the peripheral bus clock is stopped
and internal logic states are not retained. After an exit from this type of stop mode, all
registers are reset to their default values, and the SPI module must be reinitialized.
31.4.12 Reset
The reset values of registers and signals are described in the Memory Map and Register
Descriptions content, which details the registers and their bitfields.
• If a data transmission occurs in slave mode after a reset without a write to
SPIx_DH:SPIx_DL, the transmission consists of "garbage" or the data last received
from the master before the reset.
• Reading from SPIx_DH:SPIx_DL after reset always returns zeros.
Chapter 31 Serial Peripheral Interface (SPI)
MKW01Z128 MCU Reference Manual, Rev. 3, 04/2016
Freescale Semiconductor, Inc.
611
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