mc9s08qg8 Freescale Semiconductor, Inc, mc9s08qg8 Datasheet - Page 223

• Manufacturer Part Number: mc9s08qg8
• Description: Hcs08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

When CPHA = 1, the slave begins to drive its MISO output when SS goes to active low, but the data is not
defined until the first SPSCK edge. The first SPSCK edge shifts the first bit of data from the shifter onto
the MOSI output of the master and the MISO output of the slave. The next SPSCK edge causes both the
master and the slave to sample the data bit values on their MISO and MOSI inputs, respectively. At the
third SPSCK edge, the SPI shifter shifts one bit position which shifts in the bit value that was just sampled,
and shifts the second data bit value out the other end of the shifter to the MOSI and MISO outputs of the
master and slave, respectively. When CHPA = 1, the slave’s SS input is not required to go to its inactive
high level between transfers.
Figure 15-11
shown for reference with bit 1 starting as the slave is selected (SS IN goes low), and bit 8 ends at the last
SPSCK edge. The MSB first and LSB first lines show the order of SPI data bits depending on the setting
in LSBFE. Both variations of SPSCK polarity are shown, but only one of these waveforms applies for a
specific transfer, depending on the value in CPOL. The SAMPLE IN waveform applies to the MOSI input
of a slave or the MISO input of a master. The MOSI waveform applies to the MOSI output pin from a
master and the MISO waveform applies to the MISO output from a slave. The SS OUT waveform applies
to the slave select output from a master (provided MODFEN and SSOE = 1). The master SS output goes
to active low at the start of the first bit time of the transfer and goes back high one-half SPSCK cycle after
Freescale Semiconductor
(MISO OR MOSI)
(MASTER OUT)
(REFERENCE)
(SLAVE OUT)
SAMPLE IN
MSB FIRST
BIT TIME #
(CPOL = 0)
(CPOL = 1)
LSB FIRST
(MASTER)
(SLAVE)
SS OUT
SPSCK
SPSCK
SS IN
MOSI
MISO
shows the clock formats when CPHA = 0. At the top of the figure, the eight bit times are
MC9S08QG8 and MC9S08QG4 Data Sheet, Rev. 1.01
Figure 15-10. SPI Clock Formats (CPHA = 1)
BIT 7
BIT 0
1
BIT 6
BIT 1
2
...
...
...
BIT 2
BIT 5
6
Serial Peripheral Interface (S08SPIV3)
BIT 1
BIT 6
7
BIT 0
BIT 7
8
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