
Serial Peripheral Interface Module (SPI)
MC68HC08LK60 MC68HC908LK60 Advance Information Data Sheet, Rev. 1.1
160
Freescale Semiconductor
13.9 Resetting the SPI
Any system reset completely resets the SPI. Partial resets occur whenever the SPI enable bit (SPE) is
low. Whenever SPE is low, the following occurs:
The SPTE flag is set.
Any transmission currently in progress is aborted.
The shift register is cleared.
The SPI state counter is cleared, making it ready for a new complete transmission.
These items are reset only by a system reset:
All control bits in the SPCR register
All control bits in the SPSCR register (MODFEN, ERRIE, SPR1, and SPR0)
The status flags SPRF, OVRF, and MODF
By not resetting the control bits when SPE is low, the user can clear SPE between transmissions without
having to set all control bits again when SPE is set back high for the next transmission.
By not resetting the SPRF, OVRF, and MODF flags, the user can still service these interrupts after the
SPI has been disabled. The user can disable the SPI by writing 0 to the SPE bit. The SPI can also be
disabled by a mode fault occurring in an SPI that was configured as a master with the MODFEN bit set.
13.10 Wait Mode
The SPI module remains active after the execution of a WAIT instruction. In wait mode, the SPI module
registers are not accessible by the CPU. Any enabled CPU interrupt request from the SPI module can
bring the MCU out of wait mode.
If SPI module functions are not required during wait mode, reduce power consumption by disabling the
SPI module before executing the WAIT instruction.
13.11 SPI During Break Interrupts
The system integration module (SIM) controls whether status bits in other modules can be cleared during
the break state. The BCFE bit in the SIM break flag control register (SBFCR) enables software to clear
To allow software to clear status bits during a break interrupt, write a logic 1 to the BCFE bit. If a status
bit is cleared during the break state, it remains cleared when the MCU exits the break state.
To protect status bits during the break state, write a logic 0 to the BCFE bit. With BCFE at logic 0 (its
default state), software can read and write I/O registers during the break state without affecting status bits.
Some status bits have a 2-step read/write clearing procedure. If software does the first step on such a bit
before the break, the bit cannot change during the break state as long as BCFE is at logic 0. After the
break, doing the second step clears the status bit.
Since the SPTE bit cannot be cleared during a break with the BCFE bit cleared, a write to the transmit
data register in break mode does not initiate a transmission nor is this data transferred into the shift
register. Therefore, a write to the SPDR in break mode with the BCFE bit cleared has no effect.