Freescale Semiconductor, Inc.
Serial Peripheral Interface (SPI)
SPI Error Conditions
11.7 SPI Error Conditions
These conditions produce SPI system errors:
• Bus contention caused by multiple master SPIs (mode fault error)
• Writing to the SPDR during a transmission (write-collision error)
• Failing to read the SPDR before the next incoming byte sets the
SPIF bit (overrun error)
11.7.1 Mode Fault Error
A mode fault error results when a logic 0 occurs on the PD5/SS pin of a
master SPI. The MCU takes these actions when a mode fault error
occurs:
• Puts the SPI in slave mode by clearing the MSTR bit
• Disables the SPI by clearing the SPE bit
• Sets the MODF bit
11.7.2 Write Collision Error
Writing to the SPDR during a transmission causes a write collision error
and sets the WCOL bit in the SPSR. Either a master SPI or a slave SPI
can generate a write collision error.
• Master — A master SPI can cause a write collision error by writing
to the SPDR while the previously written byte is still being shifted
out to the PD3/MOSI pin. The error does not affect the
transmission of the previously written byte, but the byte that
caused the error is lost.
• Slave — A slave SPI can cause a write collision error in either of
two ways, depending on the state of the CPHA bit:
– CPHA = 0 — A slave SPI can cause a write collision error by
writing to the SPDR while the PD5/SS pin is at logic 0. The
error does not affect the byte in the SPDR, but the byte that
caused the error is lost.
MC68HC705C8A — Rev. 3
MOTOROLA
Technical Data
Serial Peripheral Interface (SPI)
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