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35.2.2 Modes of operation
The SPI functions in the following three modes.
• Run mode
This is the basic mode of operation.
• Wait mode
SPI operation in Wait mode is a configurable low power mode, controlled by the
SPISWAI bit located in the SPIx_C2 register. In Wait mode, if C2[SPISWAI] is
clear, the SPI operates like in Run mode. If C2[SPISWAI] is set, the SPI goes into a
power conservative state, with the SPI clock generation turned off. If the SPI is
configured as a master, any transmission in progress stops, but is resumed after CPU
enters Run mode. If the SPI is configured as a slave, reception and transmission of a
byte continues, so that the slave stays synchronized to the master.
• Stop mode
To reduce power consumption, the SPI is inactive in stop modes where the peripheral
bus clock is stopped but internal logic states are retained. If the SPI is configured as a
master, any transmission in progress stops, but is resumed after the CPU enters run
mode. If the SPI is configured as a slave, reception and transmission of a data
continues, so that the slave stays synchronized to the master.
The SPI is completely disabled in Stop modes where the peripheral bus clock is
stopped and internal logic states are not retained. When the CPU wakes from these
Stop modes, all SPI register content is reset.
Detailed descriptions of operating modes appear in
.
35.2.3 Block diagrams
This section includes block diagrams showing SPI system connections, the internal
organization of the SPI module, and the SPI clock dividers that control the master mode
bit rate.
35.2.3.1 SPI system block diagram
The following figure shows the SPI modules of two MCUs connected in a master-slave
arrangement. The master device initiates all SPI data transfers. During a transfer, the
master shifts data out (on the MOSI pin) to the slave while simultaneously shifting data
Chapter 35 Serial Peripheral Interface (SPI)
KL27 Sub-Family Reference Manual , Rev. 5, 01/2016
Freescale Semiconductor, Inc.
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