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16-Bit Serial Peripheral Interface (S08SPI16V1)
MC9S08JS16 MCU Series Reference Manual, Rev. 4
208
Freescale Semiconductor
13.4.9.2
SPI in Wait Mode
SPI operation in wait mode depends upon the state of the SPISWAI bit in SPI Control Register 2.
•
If SPISWAI is clear, the SPI operates normally when the CPU is in wait mode
•
If SPISWAI is set, SPI clock generation ceases and the SPI module enters a power conservation
state when the CPU is in wait mode.
— If SPISWAI is set and the SPI is configured for master, any transmission and reception in
progress stops at wait mode entry. The transmission and reception resumes when the SPI exits
wait mode.
— If SPISWAI is set and the SPI is configured as a slave, any transmission and reception in
progress continues if the SPSCK continues to be driven from the master. This keeps the slave
synchronized to the master and the SPSCK.
If the master transmits data while the slave is in wait mode, the slave will continue to send out
data consistent with the operation mode at the start of wait mode (i.e., if the slave is currently
sending its SPIDH:SPIDL to the master, it will continue to send the same byte. Otherwise, if
the slave is currently sending the last data received byte from the master, it will continue to send
each previously receive data from the master byte).
NOTE
Care must be taken when expecting data from a master while the slave is in
wait or stop3 mode. Even though the shift register will continue to operate,
the rest of the SPI is shut down (i.e. a SPRF interrupt will not be generated
until exiting stop or wait mode). Also, the data from the shift register will
not be copied into the SPIDH:SPIDL registers until after the slave SPI has
exited wait or stop mode. A SPRF flag and SPIDH:SPIDL copy is only
generated if wait mode is entered or exited during a tranmission. If the slave
enters wait mode in idle mode and exits wait mode in idle mode, neither a
SPRF nor a SPIDH:SPIDL copy will occur.
13.4.9.3
SPI in Stop Mode
Stop3 mode is dependent on the SPI system. Upon entry to stop3 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 stop mode, the
transmission is frozen until the CPU exits stop mode. After stop, data to and from the external SPI is
exchanged correctly. In slave mode, the SPI will stay synchronized with the master.
The stop mode is not dependent on the SPISWAI bit.
In all other stop modes, the SPI module is completely disabled. After stop, all registers are reset to their
default values, and the SPI module must be re-initialized.
13.4.9.4
Reset
The reset values of registers and signals are described in
Section 13.3, “Register Definition
.” which details
the registers and their bit-fields.
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