Freescale Semiconductor HCS08 Series, Reference Manual

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16-Bit Serial Peripheral Interface (S08SPI16V1)
MC9S08JS16 MCU Series Reference Manual, Rev. 4
204 Freescale Semiconductor
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 CPHA = 1, the slave’s SS input is not required to go to its inactive
high level between transfers.
Figure 13-14 shows the clock formats when SPIMODE = 0 and CPHA = 0. At the top of the figure, the
eight bit times are 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 the end of the eighth bit time of the transfer. The SS IN waveform applies to the slave
select input of a slave.
Figure 13-14. SPI Clock Formats (CPHA = 0)
BIT TIME #
(REFERENCE)
MSB FIRST
LSB FIRST
SPSCK
(CPOL = 0)
SPSCK
(CPOL = 1)
SAMPLE IN
(MISO OR MOSI)
MOSI
(MASTER OUT)
MISO
(SLAVE OUT)
SS OUT
(MASTER)
SS IN
(SLAVE)
BIT 7
BIT 0
BIT 6
BIT 1
BIT 2
BIT 5
BIT 1
BIT 6
BIT 0
BIT 7
1 2 6 7 8 ...
...
...