mc68hc908mr24 Freescale Semiconductor, Inc, mc68hc908mr24 Datasheet - Page 261

• Manufacturer Part Number: mc68hc908mr24
• Description: M68hc08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

MC68HC908MR24 — Rev. 4.1
Freescale Semiconductor
NOTE:
must read the receive data register before another full byte enters the
shift register.
The maximum frequency of the SPSCK for an SPI configured as a slave
is the bus clock speed (which is twice as fast as the fastest master
SPSCK clock that can be generated). The frequency of the SPSCK for
an SPI configured as a slave does not have to correspond to any SPI
baud rate. The baud rate only controls the speed of the SPSCK
generated by an SPI configured as a master. Therefore, the frequency
of the SPSCK for an SPI configured as a slave can be any frequency
less than or equal to the bus speed.
When the master SPI starts a transmission, the data in the slave shift
register begins shifting out on the MISO pin. The slave can load its shift
register with a new byte for the next transmission by writing to its transmit
data register. The slave must write to its transmit data register at least
one bus cycle before the master starts the next transmission. Otherwise,
the byte already in the slave shift register shifts out on the MISO pin.
Data written to the slave shift register during a transmission remains in
a buffer until the end of the transmission.
When the clock phase bit (CPHA) is set, the first edge of SPSCK starts
a transmission. When CPHA is clear, the falling edge of SS starts a
transmission. See
If the write to the data register is late, the SPI transmits the data already
in the shift register from the previous transmission.
SPSCK must be in the proper idle state before the slave is enabled to
prevent SPSCK from appearing as a clock edge.
Serial Peripheral Interface Module (SPI)
13.6 Transmission
Serial Peripheral Interface Module (SPI)
Formats.
Advance Information
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